Building Automation Systems (BAS)DDC Controls Systems Quickpage Jump Links

DDC Controls Overview

The Basic DDC Controls System Loop for HVAC Controls

DDC Controls System Responses for HVAC Controls

DDC Controls Page 2: The Technical Aspects of DDC

DDC Controls Page 3: Variable Air Volume (VAV) Systems

DDC Controls Page 4: DDC and Economizers

DDC Controls Page 5: DDC Programming and Logic

DDC Controls Related Links

DDC Systems Overview

 

Many people wonder what Building Automation Systems do. Building Automation Systems are mainly used in commercial HVAC control systems and energy management system applications. Building Automation itself is an energy management system which saves management companies and building owners by efficiently controlling air conditioning and heating comfort systems. BAS is where mechanical and electrical systems and equipment are joined with microprocessors that communicate with each other and possibly to a computer. This computer and controllers in the building automation system can be networked to the internet or serve as a stand alone system for the local peer to peer controller network only. Additionally, the BAS controllers themselves do not need a computer to operate efficiently as many of these controllers are designed to operate as stand-alone controllers and control the specific equipment they are assigned to control. With a few exceptions, each building automation controller has their own program and has the ability to communicate to other DDC building automation controllers. It is important for the building automation system controllers to communicate to each other. If the network fails for whatever reason then the system may still function (because the BAS controllers in building automation systems are stand-alone) but it will not function as efficiently as designed. Building Automation Systems grows more and more complex as time passes but it will save in energy and maintenance costs if installed and programmed properly. Energy Management Systems and Building Automation Systems (can be one in the same) are definitely the way of the future and are replacing older less efficient systems everyday.

A set-up in a multi-story automated building would have many building automation controllers serving different types of air conditioning and heating equipment (BAS is not limited to just hvac applications). Every building is different and it is important for the BAS engineer to select the proper HVAC BAS control system and programs to control the various types of HVAC systems in a particular automated building. For building automation systems to be effective, it is important that the BAS system is installed and tuned properly. Some advantages of a good HVAC BAS building automation system are:

o Building Automation System (BAS) should allow the owner to set up schedules of operation for the equipment and lighting systems so that energy savings can be realized when the

building or spaces in the building are unoccupied.

o Building Automation System (BAS) should allow the equipment optimal start with adaptive learning. Optimal start is allowing the equipment to be brought on in an ordered

and sequential manner automatically on a schedule before the building is reoccupied so that space set points can be realized before occupation. Adaptive learning allows the system to compare space temperature, outside air conditions, and equipment capabilities so that the equipment can be turned on at an appropriate time to ensure space set points are achieved before occupation.

o Building Automation System (BAS) should have trim and respond capabilities. Based on zone demand the set point for various heating and cooling sources will change

according to demand from the zones. In a VAV system all the VAV boxes are served from a

o central air handling unit. If all the zones are at set point then the supply air temperature set point of the air handler is automatically changed to prevent mechanical cooling

from occurring when it is unnecessary. When the zones grow warmer the supply air temperature set point is automatically lowered to allow mechanical cooling to satisfy demand. Older systems have a single supply air temperature set point of 55° Fahrenheit which requires the compressors to cycle even when it is not necessary.

DDC Panel being Terminated

BAS Controlled Actuators Controlling a Hot Water Bypass Valve

o Building Automation System (BAS) should have the ability to monitor energy usage including the ability to meter electric, gas, water, steam, hot water, chilled water, and fuel

oil services.

o Building Automation System (BAS) in conjunction with the appropriate mechanical system set-up should offer economizing based on enthalpy calculations and/or CO2 set

point control.

o Building Automation System (BAS) should have such BAS control algorithms as reset schedules for heating plants, static pressure control, and other systems where energy

savings can be realized through these predictive programs.

o Building Automation System (BAS) should offer load shedding when power companies are at peak demand and need business and industry to cut back on power usage to

prevent brown outs. Building Automation Systems allow the owner to cycle various things off like water heaters or drinking fountains where use of these things will not be noticed even though they are off.

o Building Automation System (BAS) should offer the ability to send alarms via email, pager, or telephone to alert building managers and/or technicians of developing problems

and system failures.

o Management companies who acquire a good building automation system (BAS) can have BAS set up to bill tenants for energy usage.

o Building Automation Systems (BAS) should have the communications abilities to be integrated with other building automation control systems and TCP/IP. BACnet compatible or other open source communication protocol is a plus.

The Basic DDC Control Loop

To understand Direct Digital Control (DDC) we must understand the basic control loop. Even the most adept HVAC controls technicians benefit in their work from going back to the basic control loop to solve problems or break down and understand complex DDC control algorithms. For a basic DDC Controls or building automation control loop we need three things:

1. Input from a sensor or device. This can be analog or digital. (See DDC/Building Automation page two for descriptions of analog and digital). In this step we are Measuring temperature or C.F.M.'s (any variables) and collecting data. DDC building automation inputs basically measure a medium or monitor the HVAC systems such as smoke detectors and high/low limit switches. DDC inputs measure temperature, humidity, pressure, current, wattage, and air and water flow among other things.

2. A DDC or building automation controller to process information and which holds the logic or programming. In this step the DDC or building automation controller is processing the information from the input device(s) and based on the algorithm, possibly sending an output signal to a device to take appropiate action if necessary. The input device(s) does not need to be hard wired to the local equipment controller nor does an output response from the local equipment DDC building automation controller going to effect the DDC building automation controllers local equipment. Over a communication trunk the DDC or building automation controller can receive input signals from distant automation controllers and issue output commands to those same or other distant building automation or DDC automation controllers. It really depends on the program and set-up of the entire system in the algorithms of the building automation system as a whole.

3. The actual device being controlled based on what the input is feeding to the DDC controls controller. In this step the controlled device is taking action to maintain the program based on program variables. Output devices can be damper actuators, valve actuators, relays (electrical and or pneumatics (p-e or e-p), variable frequency or speed drives, compressors, blowers, and pumps.

Basic DDC Control Loop

Example of a DDC Controls Loop: A VAV box is reading 600 C.F.M.'s and the zone temperature is 68 degrees F. The controller takes this input information and processes it based on pre-programmed set points. In this situation the zone is too cold so the DDC controller sends an output signal to the damper actuator to close it (some to maintain a minimum heating C.F.M. set point), energize a heating relay for heat and (with a parallel box) turn the fan on. (For more on VAV boxes see DDC/Building Automation (BAS) page 3). Because the output device is taking an action it is reasonable to assume that our input sensor variables are going to change. The process starts all over again until all set points in the DDC building automation algorithm are satisfied.

DDC Control Responses

DDC building automation algorithms contain what is called control responses. This is built into the logic and is responsible for the output to the controlled device. Some of these control responses prevent overshooting and/or undershooting. In these control responses we have five different responses:

o two-position control - either open or closed (can utilize upper and lower limits).

o floating control - example: an actuator controlled vortex damper that moves within a setpoint range to control

static pressure. Floating control commonly uses deadbands. In the example above, when the static pressure is in the deadband, the damper does not move.

o proportional control (p)*

Solid State PCBs with Processors that have the capability

to communicate with other DDC

controllers throughout the

building

o proportional plus integral (pi)*

o proportional plus integral plus derivative (pid) *

*Proportional (P), proportional plus integral (PI), and proportional plus integral plus derivative (PID) control responses are very complex algorithms. To read a detailed report on these

algorithms and how they work click here

DDC Start-up Tech's Office with a View

HVAC Control and Direct Digital Controls (DDC) Page Two

HVAC Control DDC Controls and Building Automation Systems Quickpage Jump Links

Technicial Aspects of DDC

DDC/Building Automation Wiring Standards

DDC Page One: What it should do?

DDC HVAC COntrol Page Three: VAV Systems

DDC HVAC Control Page Four: DDC and Economizers

The (Field) Technical Aspects of DDC HVAC Control

 

A HVAC technician who knows nothing about DDC controls or HVAC control systems would wonder how these hvac control systems work. To understand DDC controls and hvac controls, one must understand basic electricity and circuits. Starting with a large commercial VAV air handling unit with three stages of DX cooling and add all the necessary hvac ddc control points. We have variable frequency drives (VFD's) on the return and supply blower fans. There is a mixed air damper which closes off the return and opens up to outside air for economizing and CO2 control. Static pressure control will be achieved with a duct pressure transducer and the DDC HVAC control program through the frequency drives and blower motors. DDC needs to monitor supply air temperature, mixed air temperature, and return air temperature along with outside air and outside humidity. We will also monitor the duct smoke detectors and a freezestat for safety reasons. This is the set-up and we need to make it work. We need to get a point count and set-up our inputs and outputs.

Digital or Binary Outputs

1. Compressor Stage One 2. Compressor Stage Two 3. Compressor Stage Three 4. Supply VFD Start/Stop 5. Return VFD Start/Stop

Analog Outputs

1. Supply VFD Speed 2. Return VFD Speed 3. Mixed Air Damper

Binary or Digital Inputs

1. Smoke Detector

DDC HVAC Control Panel in the Process of Being Wired

2. Supply Fan Status 3. Compressor Status (Only one compressor status for the first stage. We assume this compressor has two unloaders for the other two stages.) 4. Freezestat

Analog Inputs

1. Supply Air Temperature 2. Return Air Temperature 3. Mixed Air Temperature 4. Duct Static pressure 5. Outside Air (this point along with humidity can be networked across a comm trunk from a distant controller. If the network option is chosen these two points would be analog

network inputs and hard wiring at this controller would be unnecessary.) 6. Humidity 7. Supply VFD Feedback 8. Return VFD Feedback

Now, your asking yourself what analog, and binary, and digital inputs and outputs are?

o Digital or Binary Outputs - Digital and binary are the same. It simply means either

on or off, 0 or 1. With DDC control these are either dry contacts or triacs. So with our compressor start/stop above we simply use DDC HVAC controls to energize a relay that starts or stops the compressor starter. These contacts are typically rated for 24 volts but may also use 120 volts depending on the manufacturer and the ratings of the dry contacts and/or triacs. Again with the VFD's we are simply energizing a relay that starts and/or stops the drive(s). These (digital or binary) contacts can also be used for Pulse Width Modulation (PWM) control.

o Analog Outputs - This is simply a modulating signal from DDC

o to a particular device or piece of equipment. Our drives, depending on how they are set

up in their local parameter programming will need a signal to tell it how fast to go. We want these drives to speed up and slow down according to what our static pressure set point is set at. There are three different typical signals we can send to these drives from DDC. These are a 4-20 Milliamp signal, a 0-10 volt DC signal, or a 2-10 volt DC signal. To keep it simple we'll set both drives and DDC up for a 0-10 volt DC signal. This is an output signal from DDC and an input signal to the drive. If we send 0 volts to the drive it will run at minimum, if we send 10 volts to the drive it will run at maximum. If we send it 5 volts it will run at half speed and so on and so forth depending on what the program calls for the output to send to the drive. These analog outputs can also be used to control SCR's for resistive heating loads.

o Binary or Digital Inputs - Again, binary and digital are the same. Some DDC

manufacturers use binary and some use digital when they describe their inputs and outputs. This is where DDC monitors some dry contacts like the smoke detector. These contacts are normally closed and when the detector detects smoke the contacts open. DDC sees this and stops all blowers and sends alarms to the appropriate sources. (We don't necessarily rely on DDC to stop all the blowers. There should be a hard wired interlock that will stop all blowers if the smoke detector alarms.) The supply fan and compressor status inputs can come from either contacts on a CT or from aux contacts on the appropriate starters. Depending on how the program is set up, DDC simply wants to see an open or closed position from these sources.

o Analog Inputs - Again, an analog signal is a modulating signal. In this case, we have analog inputs. Input to DDC from a device or piece of equipment. Our temperature

sensors are usually thermistors. Depending on the temperature, the resistance of a thermistor will change. DDC sends a small amount of current through the thermistor circuit. DDC will take the input current coming back through the thermistor circuit and translate it into a temperature. This is done in the program through tables in the database which are matched up to the rated resistance/ temperature of the thermistor. For the duct pressure transducer we are going to get a different type of signal back to DDC. We are going to power the transducer up with a separate 24 volts. According to different manufacturers, this 24 volts can be either AC or DC (read the instructions for the device). There may be optional settings on the transducer allowing you send (from the device) either a milliamp or a voltage signal to the input of DDC. For simplicities sake we'll select a 0-10 volt signal from the device to the input of DDC. There should be range settings on both the device and in the DDC program. These settings should be synchronized. Let us say for example that the range setting is 0-10 inches H2O. Therefore, with a 0-10 signal setting at the device and configured in DDC, when we get a 0 volt signal back from the device we have 0 inches H2O pressure. When we get 5 volts back from the device we have a pressure of 5 inches H2O and so on and so forth as the pressure changes so does the voltage coming from the device to DDC which will translate that into a pressure.

HVAC Direct Digital Controls (DDC) Variable Air Volume Systems (VAV's)

HVAC DDC Controls Variable Air Volume VAV Box Quickpage Jump Links

DDC Controls Variable Air Volume Systems (VAV's)

DDC Controls Building Automation Resources

DDC HVAC Controls Page One: What it should do?

DDC HVAC Controls Page Two: The (Field) Technical Aspects of DDC Controls

DDC HVAC Controls Page Four: DDC and Economizers

DDC Controls Variable Air Volume Systems (VAV's)

Variable Air Volume (VAV) systems are the best way to zone especially in large buildings. A VAV system with the proper controls and set-up will help the building owner realize large savings in energy usage. There are many VAV systems out there set

Variable Frequency Drives

up in different ways. The most common set-up (for DDC) are, of course, usually the cheapest to install. They have an air handler (DX or Chilled Water) which supplies the VAV Boxes with a fixed pressure and temperature of conditioned air. The VAV Boxes have electric reheat which will heat the air if that particular zone calls for heat (it is not uncommon to also find VAV boxes that have hot water reheat although this usually cost more to install but can save in energy costs).

The three main types of VAV boxes available are series, parallel boxes (both these boxes (series and parallel) are fan powered) and just a plain old VAV without a fan. Either type of box can offer zone comfort and energy savings if the proper controls are installed, they have the appropriate programming for sequence of operation, and the system is properly balanced and calibrated. All that being assumed, let's look at a sequence of operation for a DDC controlled VAV box. We start at the thermostat which is reading the zone temperature. If the zone temperature is too cold the DDC backs down on the damper which allows air from the primary source (VAV AHU) to feed the zone. Depending if the box is parallel or series then the blower fan kicks on. This allows air from the plenum (or above ceiling) to be redistributed into the zone (this air is usually warmer than the primary air supply). If the zone temp continues to drop then DDC will close the damper to minimum position (not closed but an engineered rate of CFM minimum flow) maximizing the use of warmer plenum air and activate electric or hydronic heat. Additionally, in the background, the zone controller is sending a heat request back through the network to the AHU equipment controller. As long as the equipment controllers (which is receiving input back from all the zone controllers) does not have any requests for cooling then it should adjust the Supply Air Temperature set point up (with the proper programming). This prevents the compressors (or chilled water valves from opening) from cycling using unnecessary energy. Additionally, as more zones call for heat and their particular dampers begin closing, the static pressure will rise. Through DDC, the variable frequency drives should slow the speed of the AHU blower allowing the static pressure to settle at a predetermined pressure. This application uses only the amount of energy necessary to keep the zones satisfied and is far better than systems which used to run flat out with little control. Note that some systems do not have variable frequency drives to control static pressure but use vortex dampers on the blowers.

Fan Powered VAV Boxes

Additionally there are VAV boxes that are fan powered and there are VAV boxes that are not fan powered. The main purpose of fan powered VAV boxes is to make use of the plenum air above the ceiling where the fan powered VAV box is located. This air is

usually warmer than the air supplied by the VAV air handler. So in the sequence of operation for a fan powered VAV box, and a non fan powered VAV box, would include closing the damper to allow minimal air from the air handler and at the same time energize the fan contactor so that the fan in the VAV box comes on and pulls warmer air from the plenum. Plenum air in most VAV box applications is also, usually, the return air for VAV air handling unit. When the fan in the fan powered VAV kicks on it pulls this plenum air into the VAV box where it mixes with the minimal airflow coming from the VAV air handler. Then it either hits a reheat hot water coil or electric heat strips and is warmed further to a desired supply air temperature (SAT) setpoint in the DDC program if the VAV system is so equipped. The are also other setpoints which the DDC program will monitor including CFM's. The analog signal coming from the DDC controller will modulate the damper open and close (and everywhere in between to maintain the programmed setpoint) to maintain the desired CFM's in either the fan powered VAV boxes or the non fan powered VAV boxes. Fan powered VAV boxes are used to help increase efficiency by making use of the warmer plenum air and mixing it with the cooler air handler air. It takes less BTU's to heat 70 degree air than it does to heat 60 degree air.

DDC/Building Automation Specialty Link Resources:

HVAC Direct Digital Controls (DDC) Economizer Systems HVAC DDC Controls and Building Automation Systems Quickpage Jump Links

DDC Page One: What it should do?

DDC Page Two: The (Field) Technicial Aspects of DDC

DDC Page Three: VAV Systems

DDC Page Five: DDC Programming Logic

Economizer Systems and DDC HVAC Control

Direct Digital Controls Systems in HVAC control has taken leaps and bounds in the last few years in being user friendliness, ease of designing systems, troubleshooting system problems, and increasing efficiency over the older energy managment systems. When discussing increasing efficiency of systems the idea of economizing always comes up. Economizers can be found in many different forms like using outside air when conditions are right to cool inside spaces, recovering heat loss from the relief air leaving the building, or making full use of the heat a boiler produces by recovering heat from the flue gases. There other ways to capture and conserve energy and for the sake of brevity we'll cover the basic way many buildings make use of economizers. That is using the outside air to cool the inside spaces instead of using mechanical cooling for the same thing.

First of all we have to understand that the mechanical code book requires so many changes of air per hour in commercial buildings. Many building owners rely on a manual fixed damper system to meet these requirements. Other systems have stand-alone dampers that will actuate to the open position based on certain rudimentary input devices. The accuracy of these devices and the function they serve are rarely set up properly and hardly ever calibrated to ensure they function as designed. Typically, within a year of installation they are disabled and the damper is closed off permanently in some way.

The second realization we must look at is the fact that, depending on geographical location, a building owner can save lots of money with a properly designed and calibrated energy management and control system that will allow the economizer to work through the HVAC systems direct digital control system. That a good energy management DDC system has the ability to be monitored from a remote location over the internet. That it collects trend data and proves energy savings using charts and graphs not mentioning the fact that the final proof will be the lower utility bill. That devices that are out of calibration or broken can be observed from the remote location and action taken to repair such devices. A good DDC energy managment system will do all this and more.

To properly set up an economizer so that it works as efficiently as possible we must have at least three input variables to control it. CO2 monitoring inside the space, an outisde air temperature reading, and an outside relative humidity reading. The CO2 will override everything alse if it reaches a specified setpoint in the DDC program. By monitoring CO2 inside the spaces we eliminate the need to have a minimum outside air damper position to meet the code requirements. That means that as long as the CO2 inside the spaces is below a specified amount the unit can operate and condition the inside air without any influence from the outside air because of minimum positions on the outside air damper. That saves energy cost and safely monitors the building spaces for CO2 levels. The next thing we need to make the economizer effective is an enthalpy calculation on the outside air. To get an enthalpy reading we must know what the temperature and relative humidity are outside. The DDC program will crunch the numbers and determine the enthalpy value of the outside air. Based on a predetermined setpoint the DDC program will lockout mechanical cooling and open the outside air damper to bring in cool air for the purpose of cooling the space. This feature alone has the ability to save lots of money on energy costs.

*Air Quality sensors which measure VOC's can also be used instead of CO2 sensors for this process.

One other feature which we can monitor and control with a good energy management DDC system and the economizer is building pressure. Using pressure transducers the building pressure can be controlled through DDC and the outside air damper and the relief air damper. This can be beneficial to

buildings that typically have problems with dampness and humidity levels inside the building from infiltration air. The system can be designed to maintain a slight positive pressure in the building so that damp infiltration air is eliminated. A good energy management DDC system can save lots of energy dollars and pay for itself very quickly if it is set up properly.

Additionally, it doesn't hurt to set up pressure transducers on each floor of the building to monitor building pressure. The building pressure can maintained at a slight positive pressure using the economizer and/or a make-up air unit to control the building pressure.

High Performance HVAC DDC Programming Logic and Symbols

HVAC Control DDC Logic Quickpage Jump links:

DDC Programming Logic in HVAC Control

Binary and Analog Inputs and Outputs

The And Gate

The Or Gate

The Not Gate

The "If" Logic

Low Limit Analog Logic

High Limit Analog Logic

Delay on Make Logic

Delay on Break Logic

PID Logic Block

HVAC DDC Programming Logic and Symbols PageBasic HVAC Control DDC Program Logic 101

Outside Air Intake

Outside Air Temperature and Humidty Sensor

DDC programming in HVAC Control can be rather complex especially to those who don't understand software or programming. Some DDC software and hardware manufacturers utilize symbols to build their logic programs for HVAC DDC control. Some of these logic blocks are rather complex but others are very simple. These are the basic logic blocks which, when combined, make up the DDC algorithm pr DDC control program. Everything from And gates to Or gates to Timers blocks to complex mathematical blocks allow a DDC Control programmer or DDC Control engineer to assemble programs in little time simple by arranging a set of logic blocks in a software program and then compiling this set of logic blocks into a basic machine line code and necessary tables which the casual observer and even the engineers never see. When this program is downloaded into the controller one can use the logic page in the DDC software to observe real time information from inputs to outputs to alarms and schedules. To someone skilled with this they can use the logic page in the DDC software to troubleshoot problems. It is simply a tool along with trend charts and graphics to watch the system, collect data, and make changes as necessary or to use to find a problem in the program or in the HVAC or Electrical equipment which the program is controlling. We'll start with simple blocks and work our way up to the more complex blocks. Understanding of ladder diagrams and basic electrical circuitry is necessary to follow these logic gates and symbols.

Binary Input - Analog Input - Binary Output - Analog Output

o The Binary input logic block will get an input signal of

either on or off (0 or 1 in Binary speak) from a device wired to the DDC controller. It will send an appropriate response out through other logic blocks for program processing through other logic blocks and eventually end at an output block. An example of a Binary input logic block would be a Binary input logic block which gets its input from a smoke alarm. If the contacts on the smoke alarm close the Binary input logic block becomes true and sends this through the program for the appropriate response.

o The Analog input logic block with receive an Analog

signal from a device wired to the DDC controller. (see DDC Page 2 for an explanation of Analog and Binary signals). An example of an Analog input logic block would be a logic block which gets its input from a pressure transducer. The pressure transducer will send an analog signal to the Analog input logic block and the Analog input logic block will send this information through the program logic.

o The Binary output logic block will get its instructions from other logic blocks in the DDC program and give a binary output response based on the input from the program.

An example of a Binary output logic block would be a Binary out logic block assigned to a motor start/stop. When the program called for the motor to energize the Binary output logic block would energize the output and a really would energize the motor starter.

o The Analog output logic block will do the same as the Binary output logic block except the signal coming from the Analog output logic block will be an analog signal.

An example of an Analog output logic block would be an Analog output logic block assigned to control a variable frequency drive which works off of an analog signal like 0 to 10 volts or 4 to 20 milliamps.

And Gate

The And gate is simply a series switch. In the DDC graphic to the left is an And gate and it is the same as the series switch to the right of the And gate. If a single input to the And gate is open the And gate will not allow an output. The input side of the And gate can have as many gates as necessary for proper functioning whatever is being controlled.

Or Gate

The Or gate is simply a circuit that says on or the other or both. If one or the other have an input signal to the Or gate the Or gate will allow an output. For example, you could have a three gate Or gate which would be linked to three specific alarms like the smoke detectors, the freeze stat, and the high static pressure switch. If one or the other tripped then the Or gate would send an output signal to an alarm logic block and an emergency shutdown logic block.

The Not Gate

The Not gate is a simple gate which will change a 0 input to a 1 output or a 1 input to a 0 output. It used for various logic programming to change a binary value from a 0 to a 1 or from a 1 to a 0.

If Less Than and If Greater Than Logic Blocks

This is basic line code programming that goes back to the basics of if, else, then. An example of the usage of these blocks would be if the outside air temperature was less than 65° then it is okay to use the economizer. Of course the program would have other conditions which may be linked through an And Gate logic block but the If Less Than logic block would be one of the conditions to enable the economizer. There are other If logic blocks such as If Equals to and others which can give an analog or a binary output to the program.

Low Limit Analog Logic Block

The Low Limit analog signal block will place a low limit an analog signal coming from the program going to the analog output. An example of this would be a minimum speed for a VFD or a minimum damper position for a modulating damper.

High Limit Analog Logic Block

The High Limit analog signal block will place a high limit an analog signal coming from the program going to the analog output. An example of this would a high analog limit to the analog output of a damper that you only want to open to maximum of 80%.

Delay on Make Logic Block

Every control or HVAC control technician knows the value of a Delay on Make logic block. You can delay fans and compressors using this control logic block and prevent short cycling.

Delay on Break Logic Block

Again, every control or HVAC control technician knows the value of a Delay on Break circuit in HVAC Controls. You can delay a fan shut down or damper closing using this block.

PID Logic Block

Proportional (P), Integral (I), and Derivative (PID) control responses are very complex algorithms. This is the logic block which will help the DDC control program tune the device being controlled using PID tuning calculations and parameters. This logic block allows user input to tune different devices with PID control to prevent overshoot and undershoot. It prevents devices from under responding or over responding to program inputs and allows for smoother operation based on the PID control algorithm.

High Performance HVAC Programmable Thermostats PageProgrammable Thermostats

Programmable Thermostats Page Quickpage Jumplinks

Programmable Thermostats

Honeywell Thermostat

Who Needs a Programmable Thermostat

How a Programmable Thermostat Works

Thermostat Video

Programmable Thermostat Related Links

The Programmable Thermostat - Honeywell Thermostat - Air Conditioner Thermostats

HVAC Thermostats - Honeywell Thermostats - Programmable Thermostats

Programmable thermostats can save you more than ten percent on your homes utility bills. For that reason a programmable can pay for itself within a few years depending on the type and expense of the type you purchase. I always lean towards Honeywell thermostats simply because I've seen their reliability in the field and sometimes ease of use. Among others, you can expect good quality from Honeywell thermostat products. The new, hi-tech style currently out on the market is the Honeywell touch-screen thermostat.

Honeywell Thermostat

This Honeywell thermostat is very easy to use and programm. It can be detached from its base and programmed from the comfort of the kitchen table. This Honeywell thermostat offers the home or business user a very easy way to save energy cost without the frustration of complicated programming. It is recommended, however, that a professional install this Honeywell thermostat and show you how to program it

for the first time. Additionally, for heat pump users, this Honeywell programmable thermostat has optional termination points inside it so that an outside air temperature sensor (sold separately from the thermostat) can be hooked up allowing you to program the Honeywell thermostat to shutdown the outdoor portion of the heat pump when the temperature outside falls below a certain temperature. The reason air-to-air heat pumps are so popular in the southern regions of the country is because heat pumps heat more efficiently when the outside air temperature is 35 degrees Fahrenheit and above (unless you have a geothermal heat pump). It then becomes necessary to run auxiliary heat. The way the average heat pump system works (or how they are installed) is the heat pump condenser continues to run even below the 35 degree temperature. This thermostat when used with the outside air temperature sensor will automatically shut the outside unit off, and turn on the auxiliary heating, allowing you to realize energy savings.

This outside air temperature feature on the Honeywell thermostat can also be used for display purposes only (versus a control/display point) simply for monitoring outside air temperature in your home or business. So whether you own a heat pump or a conventional system you can see what the outside air temperature is from inside the home or business with the Honeywell thermostat.

Honeywell thermostats are by far the most popular and rugged you can purchase. Honeywell thermostats lead

Honeywell VisonPro 8000

the market in thermostat sales because of their features and usability. Honeywell thermostats are highly recommended by many professionals in the HVAC field.

Who Doesn't Need a Programmable ThermostatIf you are or someone else is at home most of the day and night, you most likely do not need a programmable thermostat. Programmable thermostats are designed for the family on a regular schedule.

Who Does Need a Programmable ThermostatThose that wake at a certain time, leave the home at a certain time, return a certain time, and go to bed at a certain time (on a regular basis), will benefit from a programmable thermostat. Read the following information and see if owning a programmable thermostat will benefit you.

How the Programmable Thermostat Works

You have four settings on the (typical off the shelf) programmable thermostat. (*Some programmable thermostats require you to have a degree in rocket science to program. Probably the easiest thermostat to program I've found that is available to the general public is the Honeywell VisionPro 8000 Programmable Thermostat.) The following list assumes the season is winter.

Wake - this is the setting you want the temperature to be at when you wake. If you wake at 6 a.m. you probably want to set the wake time and temperature for 5:30 a.m. and whatever the desired temperature is for you.

Leave - this is the time the last person leaves the home for the day. If that person usually leaves at 8 a.m. then the thermostat can be set to change the temperature to say 60 degrees Fahrenheit at 7:30 a.m.

Return - this is the time that the first person arrives home for the day. If that person arrives home at 4 p.m. then the time and temperature can be set for say 70 degrees Fahrenheit at 3:30 p.m. That way when the person arrives home, the home is at the desired temperature.

Sleep - this is the time when everyone goes to bed for the night. If everyone is in bed by 10:00 p.m. then the thermostat can be set to change the temperature to a lower setting (say 60 degrees Fahrenheit) for the night.

There are, as described by the programmable thermostat labels and advertising information, thermostats that are 5-2 day programable thermostats and thermostats that are 7 day programmable. Either should allow you to tailor each day to suit your needs and schedule. Most programmable thermostats have settings for both the weekdays and weekends so on Saturday and Sunday you can tailor the programmable settings according to your comfort level and usual schedule for those

days. All programmable thermostats have options to over-ride the program for manual settings and an additional benefit to owning a programmable thermostat is that most are equipped with a compressor delay to protect your compressor from short cycling.

You can buy the Honeywell VisionPro Thermostats at Pex Supply: Buy the Honeywell VisionPro Thermostats

Great video about the different types of thermostats available and a thermostat High Performance HVAC recommends for you.

Honeywell Chronotherm Programmable Thermostat

High Performance HVAC Programmable Thermostat Information

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Thermostats Page Two | Thermostats Troubleshooting | Thermostat Wiring & Colors | Programmable Thermostat Page Top

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High Performance HVAC Air Conditioning &Heating Thermostat Troubleshooting Troubleshooting ThermostatsThermostat Troubleshooting - Thermostat Problem - Broken Thermostats

The main connection between the air conditioning and heating system and the end user is the thermostat. Beyond the air conditioning and heating thermostat many people know nothing about their systems that keep them comfortable year round. There comes a time when the thermostat has a problem or the end user wants to replace the thermostat because they think it is a broken thermostat. It is not uncommon for a person to call an HVAC contractor and tell the secretary that they think the thermostat is broken because their air conditioner or heating system does not work. In some instances this is the case while in others the thermostat is not broken but something is wrong with the air conditioning and heating equipment that needs to be repaired. In either case it is usually best to call an HVAC professional to look at the problem especially if you want to replace the thermostat. There are a few things you can check with your thermostat before you call an HVAC professional. A little thermostat troubleshooting is in order.

Honeywell VisonPro 8000 Uses Power Stealing Technology and battery Back-up

o An air conditioning and heating thermostat, even if it is a digital thermostat, is simply a temperature switch that turns the air conditioning and heating system on and off. As

with any switch it needs electricity to function or cause a function with the air conditioning and heating equipment. Most residential and light commercial thermostats are powered by 24 volts A.C. The thermostat gets this 24 volts A.C. from the air conditioning and heating equipment. Usually this power comes from an air handler in an air conditioning and heating split system and from the main unit for air conditioning and heating package systems. Check the circuit breaker for the air handler to make sure it is not tripped. Also check the power switch which should be located near the air handling unit. It is not uncommon for people to mistake these switches for a light switch and turn them off. They unknowingly just turned the power off for their air conditioning and heating equipment including their thermostat. That is when they begin to think they have a broken thermostat. If you have a digital thermostat the power display and the thermostat power display light may not function if you have this problem. Some air conditioning and heating thermostats use batteries to power the back light which takes us to number two in air conditioning and heating thermostat troubleshooting. Check the power switch and breaker to ensure the power is on before assuming you have a broken thermostat

o The back display light for the digital thermostat does not function but the air conditioning and heating system works fine. Check the batteries as some digital thermostats

require AA or AAA batteries for the back light to function on the thermostat. There are two main types of digital thermostats; Digital thermostats that use batteries for the back light to function and digital thermostats that use the power from the air conditioning and heating equipment. If you don’t know which kind of air conditioning and heating thermostat you have then open the thermostat up and look inside. If you don’t see any batteries or a battery compartment inside the thermostat then your thermostat uses power stealing technology. It is probably an older model digital thermostat and if it is a programmable thermostat then every time you lose power you will lose the program inside which takes us to the next step in air conditioning and heating thermostat troubleshooting.

o The programmable thermostat is always losing its program. This is most likely one of the older thermostats that use the power from the air conditioning and heating

equipment and every time you lose power you lose the program inside the thermostat. Programming an air conditioning and heating programmable thermostat can be a chore for many people to figure out so a problem like this can be frustrating especially if you live in an area where there are constant power failures. The only solution to this problem is to replace the programmable thermostat with one that uses power stealing technology (it uses power from your air conditioning and heating system to hold the

programs) and has a battery back-up just in case you lose power. This can save you lots of trouble and frustration in the long run keeping you from reprogramming the thermostat over and over again when power failures occur.

o If the problem is persistent with the thermostat it is important get back to thermostat basics.

1. Is the thermostat installed in the proper location. This is very important as a thermostat installed on a wall that has high heat gain or heat loss will never offer you comfort as it will react mostly to the temperature of the wall and not the air in the living space. Additionally, thermostats installed where direct sunlight can hit the thermostat is going to be a problem also. A thermostat located near an outside door or window will be affected every time the door or window is opened or closed. A thermostat should be located close to the return (where the filter is installed) so that it sense and reacts to the air returning to the air handler for conditioning. Additionally, thermostats located near heat sources like hot or cold water pipes, radiant heaters, fireplaces, electrical devices which produce heat, etc... will never offer accurate temperatures and conditioning for the space.

2. Is there a big hole behind the thermostat that will feed cool or warm drafts to the back of the thermostat? All thermostats have a hole behind them where the wires come into the thermostat from the air handling unit. Check this and if you find a big hole behind the thermostat stuff some insulation in this hole and cover it with a piece of tape. This will prevent drafts from affecting the thermostat.

3. Has the heating anticipator been properly set by a qualified air conditioning and heating technician? The heat anticipator is on mechanical non-digital thermostats and needs to be set according to the amp draw on the heating control circuit. The heat anticipator offers a small amount of energy savings and prevents thermostat overshooting for you as it shuts off the main burners because the fan will continue to run and dissipate the heat which remains in the furnace or heat. Digital and programmable thermostats have built in heating and cooling anticipators which automatically set themselves with no manual adjustments. The mechanical thermostat needs a manual adjustment and you need a tool called an amp meter to determine the proper setting. The cooling anticipator in the mechanical thermostat requires no manual adjustment.

4. If you have a mechanical thermostat with a mercury bulb switching mechanism inside it this thermostat needs to be level. If the thermostat is not level you never get an accurate temperature in the residence or business.

Other problems that can occur with your air conditioning and heating thermostat need to be discussed with an HVAC professional as these problems can be technical and require special tools to fix. It is always a wise choice to call in an HVAC professional when you have problems with your air conditioning and heating equipment including you air conditioning and heating thermostat.

High Performance HVAC: Thermostat Wiring PageHigh Performance HVAC Thermostat Links:

Programmable Thermostats Page

Thermostat Installation

Thermostats Troubleshooting

Thermostats Related Links

High Performance HVAC Thermostat Terminal Designations and Thermosat Color Chart

Thermostat Wiring and Wire Color Chart

Thermostat Terminal Designation Color of Wire and Termination

R – The R terminal is the power for the thermostat. This comes from the transformer usually located in the air handler for split systems but you may find the transformer in the condensing unit. For this reason, it is a good idea to kill the power at the condenser and the air handler before changing or

Red for the R terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding.

working on the wiring at the thermostat. If you have a package unit then the transformer is in the package unit.

RC – The RC terminal is designated for the power for cooling. Some HVAC systems use two transformers. A transformer for cooling and a transformer for heating. In this case the power from the transformer in the air conditioning system would go to the thermostat terminal. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

Red for RC terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

RH – The RH terminal is designated for the power for heating. See RC above for an explanation. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

Red for RH terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

Y – This is the terminal for cooling or air conditioning and goes to the compressor relay. Typically a thermostat wire pull is made to the air handler on split systems and then this wire is spliced for the separate wire pull which is made to the condenser. Some manufacturers put a terminal board strip near the control board in the air handler so a splice is not needed.

Yellow for Y Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

Y2 – This is the thermostat *The most common color I’ve seen

terminal for cooling second stage if your system is so equipped. Many systems only have a single compressor but if you have two compressors which should only operate off of one thermostat then you need the Y2 thermostat terminal for second stage cooling.

used for this terminal and wire designation is light blue but this varies and is completely up to the installer what color to use. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

W – This is the thermostat terminal for heating. This wire should go directly to the heating source whether it be a gas or oil furnace, electric furnace, or boiler,

White for W Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

W2 – This is the thermostat terminal used for second stage heat. There are gas furnaces with low fire and high fire and some depend on control from a two-stage heating thermostat with a W2 terminal. Heat Pumps use staging for auxiliary heat and need a W2 terminal.

*The most common color I’ve seen used for this terminal and wire designation is brown but this varies and is completely up to the installer what color to use.

G – This is the thermostat terminal used for the fan relay to energize the indoor blower fan. On a split system the blower fan is in the air handler while with a package unit the blower fan is in the outdoor package unit.

Green for G Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

C – This is the thermostat terminal which originates from the transformer and is necessary to complete the 24 volts power circuit in the thermostat but only if

C stands for common and there is no universal color used for this terminal although black is the most common color I’ve seen.

the thermostat consumes electricity for power. Many digital thermostats require 24 volts for power so the common wire is necessary.

O or B – These thermostat terminals are for heat pumps and the B thermostat terminal is used on for Rheem or Ruud and any manufacturer that energizes the reversing valve in heating mode for the heat pump. Most other manufacturers of heat pumps will utilize the reversing valve for cooling and the O thermostat terminal will be utilized for this purpose. This wire goes to outside heat pump condenser where the reversing valve is located.

Orange for O and Dark Blue for B depending on the installer of the heat pump and the manufacturer. If you have a Trane, Carrier, Goodman, Lennox, Ducane, Heil, Fedders, Amana, Janitrol, or any other manufacturer other than Rheem or Ruud you will be utilizing the orange wire for reversing valve. Rheem and Ruud will usually utilize the blue wire for reversing valve.

E – This thermostat terminal is for heat pumps and stands for Emergency Heating. If for whatever reason the heat pump condenser fails and it is necessary to run the heat there is an option on heat pump thermostats for emergency heating. Basically this simply utilizes the back-up heat source many heat pumps have to heat the home without sending a signal to the condenser to run for heat.

E – There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the E terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.

Aux – This thermostat terminal is for back-up on a heat pump and allows for auxiliary heating from the back-up heat source usually located in the air handler.

Aux - There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the Aux terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.

S1 & S2 – Some thermostats have this terminal and it used for an outdoor temperature sensor. The wire uses for this should be special shielded wire and completely separate form the other thermostat wires.

Using shielded wire prevents electromagnetic forces generated from other wires from interfering with the signal inside the shielded wire. A remote temperature sensor is a solid state device and the signal needed to get an accurate temperature is sensitive to electromagnetic forces from other wiring inside the structure.

High Performance HVAC: Thermostat Wiring PageHigh Performance HVAC Thermostat Links:

Programmable Thermostats Page

Thermostat Installation

Thermostats Troubleshooting

Thermostats Related Links

High Performance HVAC Thermostat Terminal Designations and Thermosat Color Chart

Thermostat Wiring and Wire Color Chart

Thermostat Terminal Designation Color of Wire and Termination

R – The R terminal is the power for the thermostat. This comes from the transformer usually located in the air handler for split systems but you may find the transformer in the condensing unit. For this reason, it is a good idea to kill the power at the condenser and the air handler before changing or

Red for the R terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding.

working on the wiring at the thermostat. If you have a package unit then the transformer is in the package unit.

RC – The RC terminal is designated for the power for cooling. Some HVAC systems use two transformers. A transformer for cooling and a transformer for heating. In this case the power from the transformer in the air conditioning system would go to the thermostat terminal. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

Red for RC terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

RH – The RH terminal is designated for the power for heating. See RC above for an explanation. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

Red for RH terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

Y – This is the terminal for cooling or air conditioning and goes to the compressor relay. Typically a thermostat wire pull is made to the air handler on split systems and then this wire is spliced for the separate wire pull which is made to the condenser. Some manufacturers put a terminal board strip near the control board in the air handler so a splice is not needed.

Yellow for Y Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

Y2 – This is the thermostat *The most common color I’ve seen

terminal for cooling second stage if your system is so equipped. Many systems only have a single compressor but if you have two compressors which should only operate off of one thermostat then you need the Y2 thermostat terminal for second stage cooling.

used for this terminal and wire designation is light blue but this varies and is completely up to the installer what color to use. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

W – This is the thermostat terminal for heating. This wire should go directly to the heating source whether it be a gas or oil furnace, electric furnace, or boiler,

White for W Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

W2 – This is the thermostat terminal used for second stage heat. There are gas furnaces with low fire and high fire and some depend on control from a two-stage heating thermostat with a W2 terminal. Heat Pumps use staging for auxiliary heat and need a W2 terminal.

*The most common color I’ve seen used for this terminal and wire designation is brown but this varies and is completely up to the installer what color to use.

G – This is the thermostat terminal used for the fan relay to energize the indoor blower fan. On a split system the blower fan is in the air handler while with a package unit the blower fan is in the outdoor package unit.

Green for G Terminal. *Although be aware that this may have changed especially if the person who wired the thermostat didn’t use conventional color coding. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

C – This is the thermostat terminal which originates from the transformer and is necessary to complete the 24 volts power circuit in the thermostat but only if

C stands for common and there is no universal color used for this terminal although black is the most common color I’ve seen.

the thermostat consumes electricity for power. Many digital thermostats require 24 volts for power so the common wire is necessary.

O or B – These thermostat terminals are for heat pumps and the B thermostat terminal is used on for Rheem or Ruud and any manufacturer that energizes the reversing valve in heating mode for the heat pump. Most other manufacturers of heat pumps will utilize the reversing valve for cooling and the O thermostat terminal will be utilized for this purpose. This wire goes to outside heat pump condenser where the reversing valve is located.

Orange for O and Dark Blue for B depending on the installer of the heat pump and the manufacturer. If you have a Trane, Carrier, Goodman, Lennox, Ducane, Heil, Fedders, Amana, Janitrol, or any other manufacturer other than Rheem or Ruud you will be utilizing the orange wire for reversing valve. Rheem and Ruud will usually utilize the blue wire for reversing valve.

E – This thermostat terminal is for heat pumps and stands for Emergency Heating. If for whatever reason the heat pump condenser fails and it is necessary to run the heat there is an option on heat pump thermostats for emergency heating. Basically this simply utilizes the back-up heat source many heat pumps have to heat the home without sending a signal to the condenser to run for heat.

E – There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the E terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.

Aux – This thermostat terminal is for back-up on a heat pump and allows for auxiliary heating from the back-up heat source usually located in the air handler.

Aux - There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the Aux terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.

S1 & S2 – Some thermostats have this terminal and it used for an outdoor temperature sensor. The wire uses for this should be special shielded wire and completely separate form the other thermostat wires.

Using shielded wire prevents electromagnetic forces generated from other wires from interfering with the signal inside the shielded wire. A remote temperature sensor is a solid state device and the signal needed to get an accurate temperature is sensitive to electromagnetic forces from other wiring inside the structure.