key hvac design concepts

Key HVAC Design Concepts

Agenda

• Discuss relevance of thermal enclosure system to HVAC system.• Present the three major steps to design an HVAC system.• Hold question and answer session.

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Thermal enclosure system

ThermalEnclosure

System

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• A well-insulated and air-sealed home, with good windows and doors, reduces the amount of energy needed to keep the home comfortable.

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1. Energy moves from more to less.2. Over time, differences in temperatures dissipate.


90°F - Outside

40°F

Cooler

90°F

70°F - Outside

4A cooler with ice

70°F

A cup of coffee

120°F


1. Energy moves from more to less.2. Over time, differences in temperatures dissipate.

105°F 105°F72°F

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FIBROUS NSULATION = AIR BARRIERThermal enclosure system

105°F 72°F

73°F

105°F

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• Heat transfer can be quantified in British Thermal Units (Btu’s).• 1 Btu is approximately equal to the energy in a single match.

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72°F73°F

8


105°F

72°F

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105°F

10

72°F


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105°F

72°F

Thermal defects to avoid

Poorly installed insulation12

Summary – Thermal enclosure system

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• Energy moves from more to less.• Over time, differences in temperatures dissipate.• Heat transfer can be quantified in Btu’s.• A complete thermal enclosure system is critical to creating

a home that is more comfortable using less energy.

Heating & cooling systems

Heating, Cooling, &Ventilation

System

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• Heating and cooling equipment that is:• High efficiency• Properly designed and installed• Combined with a duct system that’s

insulated, sealed, and balanced… maintains comfort with less energy.

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FIBROUS NSULATION = AIR BARRIERHeating & cooling systems

105°F

73°F

72°F

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Three major steps to design an HVAC system

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1. Calculate the heating and cooling loads.2. Select equipment that meets those loads.3. Design a duct system that gets air from the heating &

cooling equipment to the rooms in the house, and then from the rooms back to the equipment.

Step 1: Calculate Heating & Cooling Loads

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Step 1:Calculate heating & cooling loads

• Cooling load is the maximum Btu’s likely to be added to the home in a single hour during the year.

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• Heating load is the maximum Btu’s likely to be lost from the home in a single hour during the year.

35°F

72°F

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• Standard process to calculate loads.

• Provides a checklist of all input variables that can affect a home’s comfort level.

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21South-facing home North-facing home


2012 IECC

Climate Zone

CityHeating 99%

Dry Bulb(F)

Cooling 1% Dry Bulb

(F)

2 Houston 31 94

3 Las Vegas 27 107

4 Baltimore 15 91

5 Pittsburgh 7 88

6 Syracuse 2 85

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Important to document window performance characteristics

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Summary of Step 1:Calculate heating & cooling loads

• The first major step in the design process is to calculate the heating and cooling loads.

• ACCA Manual J provides a reliable standard process for calculating loads.

• By documenting and verifying major design parameters, the ENERGY STAR Certified Homes program helps ensure that the HVAC system has been designed properly.

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Step 2: Select the

Heating & Cooling Equipment

Step 2: Select equipment that meets loads

• Standard process to select equipment using the calculated loads.

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• Cooling Load – The number of btu’s per hour that is added to the home from the outdoors, people, lights, appliances, etc.

• Cooling Capacity – The number of btu’s per hour that cooling equipment can remove from the home.

• Heating Load – The number of btu’s per hour that is lost from the home because it’s cold outside.

• Heating Capacity – The number of btu’s per hour that heating equipment can add back to the home.

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Equipment capacity can be determined using manufacturer’s expanded performance data…

Step 2: Select equipment that meets loads• Select cooling equipment that can remove the number of

Btu’s calculated for the cooling load.

72°F 72°F73°F

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Step 2: Select equipment that meets loads• Select heating equipment that can add the number of

Btu’s calculated for the heating load.

72°F 72°F71°F

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Summary of Step 2: Select equipment that meets loads

• The second major step in the design process is to select equipment using the calculated heating & cooling loads.

• ACCA Manual S provides a reliable standard process for doing this and includes limitations on over-sizing.

• By requiring that equipment be selected using this process, the ENERGY STAR Certified Homes program helps ensure that the HVAC system is efficient, durable, and effective.

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Step 3: Design the Duct System

Step 3:Design the duct system

• Design a duct system that distributes air from the heating & cooling equipment to each room, and back to the equipment.

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Room A Room B

Hallway

• The airflow needed by each room is directly related to its heating and cooling load.

80 CFM 80 CFM 80 CFM

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• The airflow needed by each room is directly related to its heating and cooling load.

Load Distribution Airflow Distribution

Location%

AirflowAirflow (CFM)

Room A 10% 160 Room B 5% 80 Other 85% 1,360 Total Equipment Airflow 100% 1,600

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• Proper airflow is needed to deliver or remove the correct amount of heat from each room.

Room A – Correct Airflow

150 btu

100 btu

100 btu 100 btu

150 btu

300 btu’s out & 300 btu’s in

Room A – Incorrect Airflow

95 btu

100 btu

100 btu 100 btu

75 btu

300 btu’s out & 170 btu’s in36

• Factors that influence duct system design:


Flex vs. rigid duct type

Duct turns

Duct diameter

Duct length

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• Duct length• Duct diameter• Duct type

• Duct turns• Other components, like

filters


A fan uses energy to push air

Like we use energy to push air into a balloon 38


The pressure inside the inflated balloon is the

Static Pressure

If the balloon has a leak, the pressure of that

moving air is theVelocity Pressure

Static Pressure = + 0.20 IWCVelocity Pressure = + 0 IWC

Static Pressure = + 0.10 IWCVelocity Pressure = + 0.10 IWC

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• Example: Duct system without registers & sealed tightly.


Air Handler

Supply Ducts

ON

OFF

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ON

OFF

Supply Register

• Example: Supply registers added to duct system.

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• Example: Return side ducts and filters add additional static pressure to the system.

ON

OFF

Return Ductwork

Filter

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• The total external static pressure of the duct system includes both the supply and return side.

ON

OFF

- 0.10

- 0.15+ 0.20

+ 0.20

0.200.200.150.100.65

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Summary of Step 3:Design the duct system

• The third major step in the design process is to design a duct system that works with the selected equipment.

• ACCA Manual D provides a reliable standard process for doing this. It ensures that the static pressure of the duct system and the air velocity are not too high.

• These requirements in the ENERGY STAR Certified Homes program help ensure that the home is efficient, quiet, and comfortable.

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Summary

• A complete thermal enclosure system is critical to creating a home that is more comfortable uses less energy.• The HVAC design process has three major steps:– Step 1 is to calculate the heating and cooling loads.– Step 2 is to select equipment with a capacity that can meet

those loads.– Step 3 is to design a duct system that can get that heated &

cooled air from the equipment to the rooms and back.• The ENERGY STAR Certified Homes program requires this

important design process to help maintain the efficiency, comfort, and quality of every certified home.

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key hvac design concepts

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