Chapter 7: Heating, Ventilation, Air Conditioning To be used with the Guide to Building Energy Efficient
Homes in Kentucky

Type of HVAC System First-rate Contractor Decisions

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

Radiant Heating Systems Advantages: • Quieter operation • Increased personal comfort at lower air temperatures • Better zoning of heat • Increased comfort from the heat

Radiant Heating Systems 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) Inside Air Water (geothermal)

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

Air Conditioner Vapor Compression Cycle Compressor

Air Conditioner Vapor Compression Cycle Fan/Condensing Coil

Air Conditioner Vapor Compression Cycle Refrigerant

Air Conditioner Vapor Compression Cycle Evaporator Coil

Air Conditioner Vapor Compression Cycle 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.
Heat Pump Gas Furnace

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

7.0
HSPF Minimum efficiency = 7.7 HSPF Medium efficiency = 8.0 HSPF High efficiency = 8.2 HSPF Variable speed heat pumps = 9.0 HSPF Geothermal heat pumps > 10.0 HSPF 10.0

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 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

Geothermal Heat Pump

Closed Loop Designs Deep well systems: • Piping loop extends several hundred feet underground ~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 • 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 • 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 78% = minimum AFUE for most furnaces 97% = AFUE for furnaces with condensing heat exchangers • The AFUE does not consider the unit’s electricity use for fans and blowers

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
Type of Treatment AFUE 0.95
Code Home ENERGY STAR ® Home *For a system in Lexington, KY
Economic Analysis of Gas Furnaces Energy Savings*($/yr) Compared to AFUE 0.80
42 31
Break-even Investment ($)
477 352

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 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

Air Conditioner Vapor Compression Cycle

Air Conditioner Vapor Compression Cycle Compressor

Air Conditioner Vapor Compression Cycle Fans

Air Conditioner Vapor Compression Cycle Pressurized Liquid piped to Air-Handling Unit

Air Conditioner Vapor Compression Cycle 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 and specific climates • In warmer climates, the SEER declines • In Climate Zone 4, the predicted SEER is approximately 5% less than the reported SEER SEER

Economics
Type of Treatment
Air Conditioner Economics
Energy Savings* ($/yr) Break-even Investment ($)
SEER 14 (3 tons) - compared to SEER 13 SEER 15 (3 tons) - compared to SEER 14 *For a system in Lexington, KY 20 32 227 363

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%

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%

Variable Speed Units Typical installation
problems
: • Improper charging of the system – For new construction, the refrigerant should be weighed in

Variable Speed Units 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

Variable Speed Units 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 = 85 Exceeds ENERGY STAR ® Home HERS = 70
HVAC System Sizing
Heating (BTU/hour) Cooling (BTU/hour) Estimated tons of cooling* Square feet/ton 52,200 31,700 3.0
667 *Estimated at 110% of calculated size. There are 12,000 Btu/hour in a ton of cooling.
38,800 25,700 2.5
800 25,700 19,800 2.0
1,000

Sizing • Latent load = amount of dehumidification needed for the home • Sensible Heating Fraction (SHF) = portion of the cooling load for reducing indoor temperatures

25% Sensible Heating Fraction
HVAC unit with 0.75 SHF
75% Cools the temperature of indoor air Latent 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)
950 1,200 1,450
Total Cooling Capacity (Btu/h)
35,800 37,500 38,800
Sensible Heating Fraction (SHF) Dry Bulb (°F) 75°F
0.58
0.61
0.64
80°F
0.71
0.76
0.81
85°F
0.84
0.91
0.96
Sample Cooling System B Data, SEER 13 Total Air Volume (cfm)
950 1,200 1,450
Total Cooling Capacity (Btu/h)
32,000 34,100 35,600
Sensible Heating Fraction (SHF) Dry Bulb (°F) 75°F
0.56
0.58
0.61
80°F
0.67
0.71
0.76
85°F
0.78
0.84
0.90

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

Leaks

Ventilation with Spot Fan

• Bathroom fans • Range hoods • Choose low sone fans rated for continuous use Spot Ventilation 91

In-Line Ventilation with Spot Fan

Central Ventilation System • “Pick-up” ducts connected to bedrooms and bathrooms • 3-speed blower 93

Spot Ventilation

Whole House Fan
Images courtesy of U.S. EPA

Supplying Outside Air from 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 • Separate duct systems • Enthalpy heat exchangers can recapture cooling energy in summer

Stale room air return ducts Heat recovery ventilator (not part of HVAC system) Exhaust air outlet Fresh air inlet 101

Sample Ventilation Plans Mechanical ventilation system plans are routine for commercial buildings

Upgraded Exhaust Ventilation

DESIGN 2 Whole House Ventilation System

Heat Recovery Ventilation System

Radon • Cancer-causing, radioactive gas • Found in soils • Is not visible • Has no odor • Has no taste

Highest potential Moderate potential Low potential Radon

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

Radon Resistant Construction • 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 • Attach a fan to the passive system to create suction to pull the radon out of the ground and exhaust through the stack

Radon Resistant Construction
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

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

Radon Resistant Construction
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