hydronic heating north seattle community college hvac program instructor – mark t. weber, m.ed....
TRANSCRIPT
Hydronic Heating
North Seattle Community College HVAC Program
Instructor – Mark T. Weber, M.Ed.
Hydronic - 1
Objectives
• After studying this chapter, you should be able to:– Describe a basic hydronic heating system– Describe reasons for a hydronic system to
have more than one zone– List four heat sources commonly used in
hydronic heating systems– Explain the difference between a wet-base
and a dry-base boiler
Objectives (cont’d.)
– State the reason a boiler is constructed in sections or tubes
– Discuss the reasons why air should be eliminated from hydronic heating systems
– Explain the effects air has on a cast-iron or steel boiler
– Describe the function of the air cushion or expansion tank
Objectives (cont’d.)
– Explain the operation of circular pumps as they apply to hydronic heating systems
– Describe the importance of the “point of no pressure change”
– Describe the purpose of limit controls and low-water cut-off devices
– State the purpose of a pressure relief valve– State the purpose of a zone valve and list
the various types available
Objectives (cont’d.)
– Explain how “outdoor reset” can be used to increase system efficiency
– Sketch a series loop hydronic heating system and a one-pipe hydronic heating system
– Explain the function of the diverter tee– Explain the differences between a two-pipe
direct-return and a two-pipe reverse-return hydronic heating system
Objectives (cont’d.)
– Explain the application that requires the use of a balancing valve
– List benefits of primary-secondary pumping– Describe the operation and function of
mixing valves– Describe the differences between radiant
and conventional hydronic heating systems– List three common types of radiant heating
system installations
Objectives (cont’d.)
– Describe a tankless domestic hot water heater used with a hydronic space-heating system
– List preventative maintenance procedures for hydronic heating
– Describe the difference between passive and active solar systems
– Describe the declination angle and the effect it has on the sun's radiation during winter and summer
Objectives (cont’d.)
– List the typical components in a liquid-based solar system and describe their function
– Describe the operation of a solar domestic hot water system
– Describe a swimming pool solar-heating system
Introduction to Hydronic HeatingWater or steam carries heat through a
piping arrangement to the areas being heated
Terminal units are located in the heated spaces
Systems can be designed to handle multiple zones
Water is heated at the boiler (gas, oil, or electric)
Introduction to Hydronic Heating (cont'd.)Boiler cycles on and off to maintain
temperatureWater is circulated through the system
with pumps
Figure 33–1 A four-zone hydronic heating system.
The Heat SourceBoiler: appliance that heats water using oil,
gas, or electricity as a heat sourceSome boilers can use more than one sourceCan supply water at various temperatures, but
most common is 180°FCast-iron boilers are the most commonly found
in residential applicationsSteel boiler: water being heated surrounds
steel tubes carrying combustion gases
The Heat Source (cont'd.)Copper water-tube boiler: low mass boiler,
smaller and with lower capacity than cast-iron or steel but efficient
The geothermal heat pump transfers heat from the earth to a water/water-antifreeze mixture and can heat water to 130°F
The Basic Hydronic SystemExpansion tank
Water expands when heated, so expansion tanks accommodate added volume to prevent excess pressure
Standard expansion tank is a large tank located above the boiler
Diaphragm-type expansion tanks have two sections separated by a semi-permeable rubber membrane One side contains pressurized air; other is open to
water circuit
Figure 33–15 Cutaway of a diaphragm-type expansion tank. Photo by Eugene Silberstein
Figure 33–16 Expansion tank data tag. Photo by Eugene Silberstein
The Basic Hydronic System (cont'd.)Calculate actual pressure required on the air
side of a diaphragm-type expansion tank:
The Basic Hydronic System (cont'd.)Circulator/centrifugal
pumpsForce hot water from heat
source through piping to heat transfer units and back to the boiler using centrifugal force
Made up of a motor, a linkage, and an impeller Figure 33–18 When the
impeller is rotated, it “throws” the water away from the center of the pump and out through the opening. Courtesy Cengage Learning 2013.
The Point of No Pressure ChangePoint in the system where the pressure, no
matter what the system is doing, remains the sameProvides a reference point for system
evaluation and a location for multiple system-component connections Desired connection point for inlet of the circulator
pump, inlet of the expansion tank, air separator, air vent, and outlet of the pressure-reducing (water-regulating) valve
Other Hydronic System ComponentsAir separator and air scoop
Air is one of the biggest enemies of a hot water hydronic heating system
Air separator separates air from water using collision and adhesion
Directional air scoops separate and remove air on horizontal stretches of pipe
Other Hydronic System ComponentsAir vent removes air from system
Can be manually operated or automaticTemperature-limiting control (aquastat)
maintains water temperature in system
Figure 33–30 Wire screen in the air separator. Photo by EugeneSilberstein
Other Hydronic System Components (cont'd.)
High-limit control shuts own the heat source if boiler water gets too hot
Water-regulating valve (pressure-reducing valve) reduces pressure of water entering the boiler to desired level
Pressure relief valve discharges excess water when expansion creates pressureSet to relieve at or below maximum working
pressure of the low-pressure boiler (30 psig)
Figure 33–41 A low-water cut-off. Photo by Eugene Silbersteinn
Other Hydronic System Components (cont'd.)
Low-water cut-off deenergizes system if level of water in system drops below desired level
Zone valves are thermostatically controlled valves that control water flow to the various zones in the systemMay be gear-motor or heat-motor operated,
and can often be opened manuallyAvailable in two-port and three-port
varieties
Other Hydronic System Components (cont'd.)
Balancing valves ensure resistance to water flow is the same in all flow pathsResistance of water flowing in system
causes frictionValves are installed in each circuit branch
Pressure differential bypass valve relieves noise and pressure from closing multiple zone valves in two-port systemsOpens incrementally as valves close
Other Hydronic System Components (cont'd.)
Flow control valve prevents water from flowing through wrong heating loop (ghost flow)
Outdoor reset control senses outdoor ambient temperature and adjusts the water temperature in the boiler
Thermostatic radiator valves are a common method for controlling temperature in each of multiple zones
Figure 33–51 Residential outdoor reset control curve. Courtesy Cengage Learning 2013
Other Hydronic System Components (cont'd.)
Finned-tube baseboard units are common terminal heating unitsHeated water flows through piping,
transferring heat to finsAir passes over hot fins and rises by
convectionSections are rated in Btu per linear foot
(Btuh/ft), determined by temperature and water flow rate
High-Temperature Hydronic Piping Systems
Consist of previously discussed components connected together
The series loop systemMost common hydronic system because of
low installation costs Like a series electric circuit, terminal units are
piped so outlet of one heat emitter is inlet of next
Main drawback is that individual temperature control for each area being heated is impossible and each terminal unit is cooler than last
High-Temperature Hydronic Piping Systems (cont'd.)
Determine amount of water flow with this formula:
High-Temperature Hydronic Piping Systems (cont'd.)
One-pipe systemOne main piping loop extends around the
occupied space and connects outlet of boiler back to boiler return
Each terminal unit connects to main loop with two tees, which may be designed for use on a one-pipe system
Proper operation relies on proper ratios of resistance between terminal unit branch and resistance to flow in pipe between the tees
High-Temperature Hydronic Piping Systems (cont'd.)
Factors to consider in laying out, evaluating, or installing a one-pipe system: Length of the terminal branch circuit, distance
between the tees, size of piping in branch circuit and between the tees, and location of the terminal unit with respect to the main loop
Diverter or Monoflo tees are special tees for one-pipe systems, designed to increase resistance in the main loop pipe section between the two tees so that more water will be directed through the terminal heating units
High-Temperature Hydronic Piping Systems (cont'd.)
The two-pipe direct-return systemUses one pipe to carry water to the terminal
units and another to carry water from the terminal units back to the boiler Terminal unit closest to the boiler will have the
shortest piping run (lowest resistance) while the unit farthest from the boiler will have the longest
High-Temperature Hydronic Piping Systems (cont'd.)
The two-pipe reverse-return systemFirst terminal unit to be supplied with water
is the last to return water to the boiler Unit with shortest supply pipe will have longest
return pipe and vice versa
High-Temperature Hydronic Piping Systems (cont'd.)
Primary-secondary pumpingInvolves at least two separate piping circuits
between the boiler and terminal unit circuits One circuit path flows from the boiler supply back
to the boiler return The secondary circuit(s) is/are connected to the
main/primary circuit and share a portion of pipingUses standard teesMixing valves combine two water streams of
different temperatures
High-Temperature Hydronic Piping Systems (cont'd.)
One of many benefits of primary-secondary pumping is that each loop can be used to supply water at different temperatures to the terminal units in that loop
Primary-secondary systems do not have expansion tanks in each of the secondary loops because the common piping between the primary and secondary loops serves as the expansion tank for that loop
Radiant, Low Temperature Hydronic Piping Systems
Rely on heating the shell of the structure as opposed to the air in that structure
The human body acts as a radiatorUnder normal conditions, the body produces
about 500 Btu/h but only requires 100 Btu/h to remain alive; typically a room temperature of 68°F allows us to shed the extra 400 Btu/h comfortably The area close to the ceiling can be cooler and
the floor should be warmer
Radiant, Low Temperature Hydronic Piping Systems (cont'd.)
Main differences between radiant heating and conventional hydronic systems:Radiant heating systems are nearly invisible
compared to conventional hydronic systemsDifferent piping materials
Radiant systems often use polyethylene (PEX) tubing instead of copper piping
Water temperature in radiant heating systems considerably lower than in conventional hydronic systems (avg. of 110°F)
Radiant, Low Temperature Hydronic Piping Systems (cont'd.)
Heat sources for radiant heating systemsGeothermal heat pump system
Use a buffer tankCopper-tube, low-mass boiler
A buffer tank is still a good ideaDirect piping
Boiler must be designed to handle potentially low temperature of water returning to the tank or provide a means to keep return-water temperature high enough to prevent flue-gas condensation
Radiant, Low Temperature Hydronic Piping Systems (cont'd.)
Radiant heat piping applicationsSlab on grade
Popular for new construction applications Spacing of PEX tubes in fresh concrete depends
on depth below concrete surface, size of tubes, type of floor, and location of tubes with respect to the outside walls of the structure
Place insulation and a vapor barrier below the concrete slab to prevent losing heat to ground
Radiant, Low Temperature Hydronic Piping Systems (cont'd.)
Thin slab Common when there is an existing floor in place
1.5-2” slab of concrete poured over tubing; completely cover PEX tubing with at least ¾” of concrete
Dry applications Staple the tubing to the bottom of the flooring
material (staple-up job) Keep staples closely spaced so that tubing is in
loose contact with floor for effective heat transfer Another concrete-free option is aluminum fins
attached to PEX tubing fed through floor joists
Radiant, Low Temperature Hydronic Piping Systems (cont'd.)
Many different piping arrangements can be used with radiant heating, including:Direct piping is the simplest configuration
Best to use a buffer tank with a boilerManually set mixing valves do not respond
to changes in water temperature or flow rate
Thermostatic mixing valves adjust internal settings to supply water at the desired temperature; prevents flue gas condensation
Combination (High- and Low-Temperature) Piping Systems
In the case where a structure has both high and low temperature heating circuits, the same boiler can be used to serve both applications using a primary-secondary pumping arrangement
Tankless Domestic Hot Water Heaters
Most oil and gas fired hot water heating boilers can be furnished with a domestic hot water heater consisting of a coil inserted into the boiler containing the domestic hot water, heating it quicklyEliminates the need for a storage tankAn efficient way to produce hot water
Solar Heating as a Supplemental Heat Source
It is estimated that two weeks of solar energy is equal to all known deposits of coal, gas, or oil
The challenge is to better harness and use this energy, for example to collect, store, and distribute solar heat
Passive Solar DesignUses nonmoving parts of a building or
structure to help provide heat or cooling or eliminate parts of a building causing inefficient heating or coolingExamples: placement of windows,
greenhouses, roof overhangs, etc.Contrast with active solar systems that use
electrical or mechanical devices to help collect, store, and distribute the sun's energy
Direct and Diffuse RadiationOnly about 0.000000045% of the sun's
energy reaches the earth as direct radiationEnergy that is reflected into space or
scattered by absorption in moisture and pollutants is called diffuse radiation
Solar Constant and Declination Angle
The rate of solar energy reaching earth's atmosphere is the same at all timesSolar constant: 429 Btu/ft²/h
Intensity of solar energy reaching the northern/southern atmospheres varies because of declination angle: 23.5°
Radiation also varies because of distance and angle of rays with regard to a particular place
Active Solar DesignUses collectors, storage systems, distribution
devices such as pumps and fans, and control systemsLiquid solar forced air space-heating systemsDrain-down systems used in areas where water
to, from, and in collectors would freeze if left in the system Circulator pumps move water from storage Alternative uses closed-collector piping with
antifreeze solution
Active Solar Design (cont'd.)Liquid collection/water storage/auxiliary
conventional hot water boiler Liquid-based solar collector may be paired with a
hot water finned-tube convector heating furnace System uses the auxiliary boiler when the storage
water is not hot enough, or may be designed as two separate systems in parallel so that both can operate at once
Solar Radiant HeatWater or antifreeze is piped through a
collector systemHeating coils may be imbedded in concrete in
the floor or plaster in ceilings or wallsNormal surface temperature is 85°F for floor
heating or 120°F for wall or ceiling panels
Solar-Heated Domestic Hot WaterMany solar systems are installed specifically
to heat or assist in heating domestic hot waterHeated collector water or antifreeze is pumped
into the heat exchanger to provide heat to the water in the tank Toxic antifreeze must be separate from water
Flat-plate liquid solar collectors use one or two panels of glass, an absorber plate, and black paint to absorb maximum heat
Solar Pool HeatingMany use the pump that circulates pool
water through the filterPool water is pumped through filtering devices,
then diverted to solar collectors to be heated before flowing back to the pool
When pool reaches desired temperature level, water bypasses collectors and returns directly to the pool
Summary
• Hydronic systems carry heated water or steam to remote locations via piping arrangements
• Boiler cycles on and off to maintain the desired water temperature in the system
• Component parts include the air separator, air vent, limit control, circulator, water regulating valve, and flow control valve
Summary (cont’d.)
• The ASME requires the installation of a pressure relief valve on all hot water boilers
• Forced air hot water unit heaters are used in commercial and industrial applications and use fans to move air across the heat exchanger surface
Summary (cont’d.)
• Common hydronic piping arrangements include the series loop system, one-pipe system, two-pipe reverse return and two-pipe direct return
• The one-pipe system uses diverter tees to balance water flow through all terminal units
Summary (cont’d.)
• Liquid solar forced air space-heating systems may use drain-down or closed-collector piping system
• Liquid solar space-heating systems may be combined with many types of conventional heating systems
• Solar heating may be used to heat domestic hot water and swimming pools
For more information please contact
Mark T. Weber
At
North Seattle Community College
WWW.NorthSeattle.edu