7. S easonal
E nergy
E fficiency
R atio
Air Conditioner Efficiencies
Minimum SEER =
10 Btu’s/Whr for central
home systems
8. Air Conditioner Efficiencies
SEERs range from 10 to
over 18 for very efficient
AC units.
Going from SEER 10 to
SEER 14 for example, will
reduce cooling energy
costs by about 30%.
10. Common Heating System Types
• Electric Strip
• Uses either baseboard
or air handler mounted
electric resistance strips
• Low installation cost
but least efficient
option.
11. Common Heating System Types
• Electric Strip
• Heat pump
• Air conditioner
refrigeration cycle in
reverse (heats home
instead of cooling it).
• Cost effective vs.
electric strip in all regions
except very warm.
12. Common Heating System Types
• Electric Strip
• Gas Furnace
• Heat pump
• Similar efficiency to heat
pumps
• Burns natural gas or
liquid propane
15. 0
1
2
3
4
5
6
7
8
9
10
S
y
s
t
e
m
E
E
R
0 5 10 15 20 25 30
Percent Leak
Replaced Air = Outside Replaced Air = Attic
Cooling System w/ Supply Leaks
Effective System EER
Source:Contracting Business Apr94,
Solv ing Leakage & Return Problems by
Duct Leakage
16. HVAC-induced infiltration
Infiltration rates - Florida Duct Study 1990
0
10
20
30
40
50
60
70
80
Number
of
houses
<0.25 0.25-
0.5
0.5-
0.75
0.75-
1.0
1.0-1.5 1.5-2.0 >2.0
air change rate
Fan off Fan on
Duct Leakage
18. Florida
50 all electric homes
13% total building
leakage in duct
system
17% savings
$200 cost
Duct Leakage Research 1990
19. Closing interior doors when AHU fan on
0.16
0.42
0.62
0.94
1.15
0
0.2
0.4
0.6
0.8
1
1.2
O
p
e
n
O
p
e
n
2
c
l
o
s
e
d
4
c
l
o
s
e
d
A
l
l
C
l
o
s
e
d
fan on
fan off
Door Closure
House
air
changes
per
hour
(ach)
20. Utility room door that swings to the
return grill.
When the system turns on, the door is
pulled to the grill, blocking air flow.
Duct Design Problems
21. Summary
• Selecting efficient air conditioning
based on your climate.
• Selecting the proper type of and
efficiency heating system for your
climate
• Designing and sealing air distribution
systems properly.
HVAC efficiency includes:
Editor's Notes
Basic split system HVAC system components and flows.
Condenser (outside unit) components of split system. Refrigerant coming from the air handler (as a gas) is compressed by the compressor and heats up as a result. The heat is removed by running the refrigerant through the heat exchange coils while the fan is running outside air through the coils. As a result, the refrigerant condenses into a high pressure liquid. The liquid refrigerant then again vaporizes and cools as it passes through the expansion valve on its way to the air handler.
Air handler (indoor unit) of split system. The cold liquid refrigerant coming from the condenser (outdoor unit) travels through the heat exchange coils while air from the house is pulled across the coil by the fan. As a result the refrigerant is warmed and the house air is cooled.
Duct system overview.
Duct system components with air handler. The air handler fan pulls air from the house through the return grille, into the return plenum and then through the cooling coils. The fan also then pushes the cooled air through the supply plenum, into the supply ducts and into the rooms.
Note that in some areas of the country air conditioning is widespread in homes while in others it is not as common.
Note to the students that the amount that will be cost effective to spend on higher efficiency systems will depend on the climate- if the air conditioner will only be used occasionally over an entire summer, it won’t be cost effective to purchase a very high SEER unit.
Again note that the type of heating system and efficiency level that will be cost effective will depend greatly on the climate.
Duct leakage is also an important efficiency factor. A supply duct disconnected from the main supply “trunk” is shown here.
Gaps at collar where a flex supply duct attaches to a supply register box.
This plot show how leaky ducts can reduce the effective efficiency of of an AC system. Typical leakage percentages in new homes are 10 to 15%, so what started as a EER (energy efficiency ratio) 10 system efficiency will actually perform like a EER 6,7 or 8 system.
As discussed earlier, infiltration is unwanted or unplanned air leakage into or out of a building through cracks and other holes in the building envelope. So infiltration also has an effect on overall efficiency. This bar chart shows that most homes tested in this study had relatively low infiltration rates (less than 0.25 air changes per hour) when the air conditioner was off, but when it was turned on, the air change rate increased to where most homes were between (0.5 and 1.5 air changes per hour). This increase was caused because of duct leakage creating increased pressures inside the home so more air leaks through the existing cracks and holes. The recommended air change rate is 0.35 air changes per hour.
Visible photo of wall section with return grille on the left and infrared (IR) photo (showing surface temperature) of the same wall on the right. White and red colors are hottest and blues are coolest in the IR photo, so this summertime photo shows that hot air is being pulled from the attic down the wall and into the air handler because of leak pathways through the wall cavity (the wall cavity should have been sealed off from the air pathway into the air handler).
Example of savings that can be found by fixing duct work. Paybacks are often less than two years; paybacks can be even shorter when ducts are installed and sealed correctly during construction. The photo on the top left suggests that having to repair duct work isn’t “pretty”- it’s bette to do it correctly in the first place.
Closing interior doors to air conditioned rooms can restrict the pathway that the air supplied to the room has to get back to the air handler. As a result when doors are closed, the individual rooms can become pressurized while the main body of the house becomes depressurized. This situation results in more outside air leaking through a home’s envelope than would have otherwise.
Click on the photo of the door in this slide to see the door swing closed, blocking airflow from the house into the return plenum and air handler. This is not a good way to design a system!
Click on the photo of the door in this slide to see the door swing closed, blocking airflow from the house into the return plenum and air handler. This is not a good way to design a system!
