Chapter 7: Heating, Ventilation, Air Conditioning To be used with the Guide to Building Energy...

Chapter 7: Heating, Ventilation, Air Conditioning

To be used with the Guide to Building Energy Efficient Homes in Kentucky

Decisions

Type of HVAC System

First-rate Contractor

Energy Efficient Home

HVAC Efficiency

Keys to obtaining design efficiency include:• Sizing the system• Proper selection and proper installation of

controls• Correctly charging the unit with proper

amount of refrigerant• Sizing and designing the layout of the

ductwork• Insulating and sealing all ductwork

Heating Systems

Types of heating systems• Forced-air• Radiant

Heat source• Furnace (gas)• Electric heat pump

Components of Horizontal Flow Forced-air System

Choices for Central, Forced-air Systems

• Fuel-fired furnaces with electric air conditioning units

• Electric heat pumps or • Dual fuel system

Best choice depends upon:― Cost― Efficiency― Annual energy use― Local price― Availability of energy sources

Radiant Heating Systems

Combine a central boiler, water heater or heat pump water heater with piping

To transport steam or hot water

Delivered via radiators or radiant floor systems


Advantages:• Quieter operation• Increased personal comfort at lower air

temperatures• Better zoning of heat• Increased comfort from the heat


Disadvantages:• Higher installation costs• No provision for cooling the

home• No filtering of the air• Difficulty in locating parts

Heat Pumps

Heat pumps move heat from one fluid to another.

Air (air-source)

Water (geothermal)

Inside Air

Heat Pumps

Air-source Heat Pumps

Most heat pumps operate:• Twice as efficiently as conventional electric

resistance heating systems• Have a 15 year life compared to 20 years

for furnaces

Air Conditioner Vapor Compression Cycle


Compressor


Fan/Condensing Coil


Refrigerant


Evaporator Coil


Duct Heater

Heat Pumps

Balance point = temperature at which heat pumps can no longer meet the heating load– Outside temperatures of 25° to 35°F

• Supplemental heat needed

Heat Pumps

Some homes use a dual-fuel system.

HeatPump

GasFurnace

Heat Pumps

• Air-source heat pumps need outdoor thermostats.– This prevents operation of the strip heater at

temperatures above 35°F.• Many mechanical and energy codes require

controls to prevent strip heater operation during weather when the heat pump alone could provide adequate heating.

Efficiency

Heating efficiency of a heat pump is measured by its Heating Season Performance Factor (HSPF).

HSPF = ratio of heat provided in Btu per hour to watts of electricity used

HSPF

Minimum efficiency = 7.7 HSPF Medium efficiency = 8.0 HSPF High efficiency = 8.2 HSPF

Variable speed heat pumps = 9.0 HSPFGeothermal heat pumps > 10.0 HSPF

7.0 10.0

HSPF

HSPF and specific climates• In colder climates, the

HSPF declines• In warmer climates, the

HSPF increases• In Climate Zone 4, in the

winter, the predicted HSPF is approximately 15% less than the reported HSPF

Geothermal Heat Pumps

• A geothermal heat pump relies on fluid-filled pipes, buried, as a source of heating in winter and cooling in summer

~54°F

http://tristate.apogee.net/geo/gocon1.asp

Geothermal Heat Pump

Deep well systems:• Piping loop

extends several hundred feet underground

Closed Loop Designs

~54°F

Closed Loop Designs

• Shallow loops are placed in long trenches, like a “slinky”

Closed Loop Designs

Geothermal Heat Pumps

• Proper installation is essential for high performance

• Longer service than air-source units

• Cost is $1,300 to $2,300 more per ton than conventional air-source heat pumps

Geothermal Heat Pump Efficiency

Coefficient of Performance (COP) = heating efficiency of a geothermal heat pump

• COP measures the number of units of heating or cooling produced by a unit of electricity

Geothermal Heat Pump Efficiency

• COP is a more direct measure of efficiency than the HSPF

• COPs are provided for different supply water temperatures–If COP = 3.0, the system would be

operating at 300% efficiency

Furnace Equipment

Which is more economical? heat pump or furnace

Variables:• Type of fuel burned• Its price• Home’s design• Outdoor climate

Furnace Operation

Furnaces require• Oxygen (for combustion)• Extra air (to vent exhaust

gases)

Furnace Operation

NON-DIRECT VENT UNITS• Common• Use the surrounding air for combustion and

exhaust venting• Problem: malfunctioning heater may allow

flue gases into the area around the furnace

Furnace Operation

DIRECT VENT OR UNCOUPLED FURNACES

• Bring combustion air into the burner area via sealed inlets that extend to outside air

• Can be in the conditioned area of a home

Furnace Operation

• New furnaces have forced draft exhaust systems–A blower propels exhaust gases out the flue

to the outdoors• Atmospheric furnaces have no forced draft fan

―Must be isolated from conditioned space

Sealed Mechanical Room Design

Measures of Efficiency

AFUE = efficiency of a gas furnace

Annual Fuel Utilization Efficiency (AFUE) = a rating which takes into consideration losses from pilot lights, start-up and stopping

AFUE

• The AFUE does not consider the unit’s electricity use for fans and blowers

78% = minimum AFUE for most furnaces

97% = AFUE for furnaces with condensing heat exchangers

AFUE

AFUE = 78%

$ .78 worth of usable heat is produced

$ .22 worth of energy is lost

AFUE

• Efficiency is highest if the furnace operates for longer periods

• Oversized units run intermittently and reduce operating efficiencies

AFUE

78% to 87% AFUE units have:• electronic ignitions • efficient heat exchangers,• better intake air controls • induced draft blowers

90% AFUE units have:•special secondary heat exchangers that cool flue gases until they partially condense•heat losses up the flue are virtually eliminated

AFUE

Condensing furnaces• A drain line must be connected to the flue to

catch condensate• With cooler exhaust gas, the flue can be made

of plastic pipe

Condensing Furnaces

Secondary heat exchanger– Increases efficiency

Pulse furnace– Achieves efficiencies over 90% using a spark

plug to explode gases, sending a shock wave out an exhaust tailpipe

– Noisy

Economic Analysis

Economic Analysis of Gas Furnaces

Type of TreatmentAFUE 0.95

Energy Savings*($/yr) Compared to AFUE 0.80

Break-even Investment ($)

Code Home 42 477

ENERGY STAR® Home 31 352

*For a system in Lexington, KY

Electric Integrated Systems

A central heat pump that provides water heating, space heating and air conditioning should:

• Have a proven track record• Have comparable price• Have a 5 year warranty• Be properly sized for both the heating and hot

water load

Unvented Fuel-fired Heaters

• Malfunction could be life threatening• Can cause serious moisture problems

Unvented heaters are NOT recommended

Unvented Heater

Direct Vent Heater

Air Conditioning

In summer, air conditioners and heat pumps work the same way to provide cooling and dehumidification.

Air Conditioner

System:• Air-handling unit houses– Evaporator coil– Indoor blower– Expansion or throttling valve

• Controls• Ductwork


Compressor


Fans


Pressurized Liquid piped to Air-Handling Unit


Evaporator Coils

Air Conditioners

• Homeowners will frequently lower the thermostat if a/c units are not providing sufficient dehumidification.– Every degree the thermostat is

lowered will increase cooling bills 3% to 7%

SEER Rating

The cooling efficiency of a heat pump or an air conditioner is rated by the Seasonal Energy Efficiency Ratio (SEER).

• SEER = a ratio of the average amount of cooling provided during the cooling season to the amount of electricity used.

SEER

National legislation mandates:• A minimum SEER 13.0 for

most residential air conditioners

• Efficiencies can exceed SEER 19.0

SEER

SEER and specific climates• In warmer climates, the

SEER declines• In Climate Zone 4, the

predicted SEER is approximately 5% less than the reported SEER

Economics

Air Conditioner Economics

Type of Treatment Energy Savings* ($/yr) Break-even Investment ($)

SEER 14 (3 tons) - compared to SEER 13 20 227

SEER 15 (3 tons) - compared to SEER 14 32 363

*For a system in Lexington, KY

Variable Speed Units

Advantages• Save energy• Quiet• Dehumidify

Proper Installation

How much lower is the operating efficiency, in hot weather, of a SEER 13 air conditioning system, with leaky ductwork?

1% to 4% lower 10% to 20% lower 25% to 40% lower Over 50%


Typical installation problems:• Improper charging of the system– For new construction, the refrigerant

should be weighed in


Typical installation problems:• Improper charging of the system• Reduced air flow– A 20% reduced air flow can drop the operating

efficiency of the unit by 1.7 SEER points


Typical installation problems:• Improper charging of the system• Reduced air flow• Inadequate air flow to the outdoor unit– Air temperatures around the unit rise, making it

more difficult for the unit to cool the circulating refrigerant

HVAC

Proper

Design

and Size

Proper Installation

Proper Operation

Sizing

• Energy efficient and passive solar homes have less demand for heating and cooling– Install smaller units that are properly sized– High efficiency systems will not provide as much

annual savings on energy bills• May not be as cost effective as in less efficient homes

Sizing

Oversized equipment• Costs more• Wastes energy• May decrease comfort– Inadequate dehumidification

Sizing

Rule of thumb• 600 square feet of cooled area per ton of air

conditioning

Sizing

Heating and cooling load calculations rely on:• Outside winter and summer design

temperatures• Size and type of construction for each

component of the building envelope• Heat given off by the lights, people and

equipment inside the house

Sizing

Equipment Sizing Comparison

Type of House Code Home HERS = 98 ENERGY STAR® Home HERS = 85Exceeds ENERGY STAR® Home

HERS = 70

HVAC System Sizing

Heating (BTU/hour) 52,200 38,800 25,700

Cooling (BTU/hour) 31,700 25,700 19,800

Estimated tons of cooling* 3.0 2.5 2.0

Square feet/ton 667 800 1,000

*Estimated at 110% of calculated size. There are 12,000 Btu/hour in a ton of cooling.

Sizing

• Latent load = amount of dehumidification needed for the home

• Sensible Heating Fraction (SHF) = portion of the cooling load for reducing indoor temperatures

Sensible Heating Fraction

75%

25%

HVAC unit with 0.75 SHF

Cools the temperature of indoor airLatent heat removal

SHF

• Many homes in Climate Zone 4 have design SHFs of 0.7– 70% sensible cooling– 30% latent

Temperature Controls

Thermostat• Programmable (setback) thermostat– Energy saver– Automatically adjust– Must be designed for the particular heating and

cooling equipment it will be controlling

Thermostat

• Centrally located• Should not receive direct sunlight or be near a

heat-producing appliance• A good location is 4 to 5 feet above the floor

in an interior hallway near a return• Interior wall on which it is installed should be

well sealed at the top and bottom

Zoned HVAC Systems

• Larger homes often use 2 or more separate heating and air conditioning units

Zoned HVAC Systems

A single system with damper control over the ductwork

1. Install a manufactured system that uses a dampered bypass duct connecting the supply plenum to the return ductwork

Automatic Zones System

Zoned HVAC Systems

2. Create two zones and oversize the ductwork 3. Use a variable speed HVAC system with a

variable speed fan for the duct system

Cooling Equipment Selection

Sample Cooling System A Data, SEER 15

Total Air Volume (cfm)

Total Cooling Capacity (Btu/h)

Sensible Heating Fraction (SHF)

Dry Bulb (°F)

75°F 80°F 85°F

950 35,800 0.58 0.71 0.84

1,200 37,500 0.61 0.76 0.91

1,450 38,800 0.64 0.81 0.96

Sample Cooling System B Data, SEER 13

Total Air Volume (cfm)

Total Cooling Capacity (Btu/h)

Sensible Heating Fraction (SHF)

Dry Bulb (°F)

75°F 80°F 85°F

950 32,000 0.56 0.67 0.78

1,200 34,100 0.58 0.71 0.84

1,450 35,600 0.61 0.76 0.90

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Ventilation and Indoor Air Quality

Ventilation• Removes stale interior air• Removes excessive moisture• Provides oxygen

Ventilation

Ventilation

Amount• 7.5 natural cubic feet per minute of fresh air

per bedroom + 1, plus additional air flow equal to (in cubic feet per minute) 1% of the house conditioned area, measured in square feet

Ventilation

7.5 cfm x (3 + 1)+ 1% of floor area (2,000) = 30 cfm + 20 cfm = 50 cfm

2,000 square foot

home3 bedrooms +

1

Ventilation with Spot Fan

91

Spot Ventilation

• Bathroom fans• Range hoods• Choose low

sone fans rated for continuous use

In-Line Ventilation with Spot Fan

93

Central Ventilation System

• “Pick-up” ducts connected to bedrooms and bathrooms

• 3-speed blower

Spot Ventilation

Whole House Fan

Images courtesy of U.S. EPA

Supplying Outside Air from Air Leaks

Where are the air

leaks?

Supplying Outside Air from Inlet Vents

Provide fresh outside air through inlet vents• Purchased from energy specialty outlets• Located in exterior walls• Control either manually or with humidity

sensors• Locate in bedroom closets with louvered

doors or high on exterior walls

Supplying Outside Air via Ducted Make-up Air

Provide fresh outside air through the ducts for a forced-air heating and cooling system

• Automatically controlled outside air damper in the return duct system

• Blower – either the air handler or a smaller unit specifically designed to provide ventilation air

Fresh Air and Dehumidification Strategies

Heat Recovery Ventilators

Air-to-air heat exchangers = heat recovery ventilators (HRV)

• Separate duct systems• Enthalpy heat exchangers can recapture cooling energy

in summer

101

Stale room air return ducts

Heat recovery ventilator (not part of HVAC system)

Exhaust air outlet

Fresh air inlet

Heat Recovery Ventilators (HRV)

Sample Ventilation Plans

Mechanical ventilation system plans are routine for commercial buildings

Upgraded Exhaust Ventilation

Whole House Ventilation System

DESIGN 2

Heat Recovery Ventilation System

Radon

• Cancer-causing, radioactive gas

• Found in soils

• Is not visible• Has no odor• Has no taste

Radon

Highest potential

Moderate potentialLow potential

Removing Radon

• Ventilate under the foundation to help remove radon and other soil gases

• More cost-effective to include any radon resistant techniques while building a home

Radon Resistant Construction


Passive• Perforated “T” fitting is

attached to a vertical plastic vent stack that penetrates the roof

• “T” is buried in gravel under the foundation slab and radon can escape

Active• Attach a fan to the

passive system to create suction to pull the radon out of the ground and exhaust through the stack


SLAB-ON-GRADE OR BASEMENT

• Use a 4 to 6 inch gravel base• Install continuous layer of 6-mil polyethylene• Stub in “T” below polyethylene that protrudes

through polyethylene and extends above poured floor height

• Pour slab or basement floor• Seal slab joints with caulk


CRAWL SPACE• Install sealed, continuous layer of 6-mil polyethylene• Install “T” below polyethylene that protrudes

through polyethylene


ALL FOUNDATIONS• Install a vertical 3-inch PVC pipe

from the foundation to the roof through an interior wall

• Connect the “T” to the vertical 3-inch PVC pipe for passive mitigation

• Have electrician stub-in junction box in attic

• Label PVC pipe “RADON” so that future plumbing work will not be tied into the stack

Testing for Radon

Test for elevated radon levels• Do-it-yourself radon test kits

are available• If high:– Easy and inexpensive to make an

active system from an existing passive system

– Add an in-line fan

Summary

Chapter 7: Heating, Ventilation, Air Conditioning To be used with the Guide to Building Energy...

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Transcript of Chapter 7: Heating, Ventilation, Air Conditioning To be used with the Guide to Building Energy...