ARCH-432
Heat Pumps and Single-zone
Systems
Attendance
What refrigerant did
these popular
“Monitor Top”
refrigerators use?
A. Freon
B. R-11
C. Sulfur Dioxide
D. Butane
E. Air
Terms
• Heat pump
– Earth-coupled
– Water source
• PTAC
• Single zone
• Rooftop
• VRF systems
Selection Criteria
• Energy Efficiency
• Acceptable comfort levels
• Flexibility
• Maintenance & Operation
• Service Life
• Indoor Air Quality
• Space
• Noise
• Zoning
• Aesthetics
• Cost
Selection Rule #1
• All systems are a compromise
Selection Rule #2
• That would include:
– Room for all HVAC and Electrical
– 4 to 6% of floor area.
Heat Pump Classifications
• Air to Air heat pumps
• Water source heat pumps
– Boiler type
– Earth coupled
Vapor Compression in the
Home
Heat Pump Cycle
Heat Pump Cycle
Exact same Vapor Compression
Cycle
The only difference is that we
have a reversing valve and an
extra thermostatic expansion
valve.
Heat Pump Cycle
Exact same Vapor Compression
Cycle
Now you are either rejecting
heat to the outdoors (typical
air-conditioning system) or
rejecting heat indoors (heat
pump mode).
Heat Pump Cycle
Exact same Vapor Compression
Cycle
Because it uses rejected heat
from the compressor, the
discharge temperature on a
heat pump is very low,
compared to a furnace
(105° F compared to 120° F)
Cooling Mode (Air to Air)
from 2009 HeatPump-Reviews.com
Heat Pump in Cooling Mode
water
loop
expansion
device
compressor
refrigerant-to-air
heat exchanger
reversing
valve
American Standard © 1999
refrigerant-to-water
heat exchanger
Point 1 At the beginning of the cycle the refrigerant (such as Freon) is in a liquid form
(gas contained under pressure becomes a liquid just like the propane in the tank). This
liquid refrigerant is very cold. It enters the evaporator coil located inside your house.
The hot air in your house moves over the coil and the air starts to lose its heat and cool
down.
Point 2 After the refrigerant leaves the indoor evaporator coil it has absorbed heat and
become gas. Just like when you heat water on the stove and it becomes steam the
refrigerant gas evaporated when it absorbed all that heat in the house (that’s why we
call this coil the evaporator).
The refrigerant enters the compressor which mechanically
pressurizes the gas. That process will increase its temperature so
the refrigerant will leave the compressor as hot gas.
Point 3 The refrigerant next moves to the condenser coil located outside the
house. Because the temperature outside is lower than the temperature of the
hot gas the heat is transferred or “rejected” from the refrigerant in the coil to
the outside air.
Point 4 The refrigerant leaves the outdoor condenser coil as warm liquid.
Now we need to make the warm liquid refrigerant cold so that it can absorb
more heat. So it goes to the metering device which drops the pressure on
the warm liquid and thus drops its temperature. The refrigerant leaves the
metering device as a cold liquid, ready to repeat the cycle again.
Heating Mode (Air to Air)
What energy sources does a water
source heat pump have in winter?
Heat Pump in Heating Mode
water
loop
expansion
device
compressor
refrigerant-to-air
heat exchanger
reversing
valve
refrigerant-to-water heat exchanger
American Standard © 1999
Look at the reversing valve it Rotates 90o , that changes the direction of the
flow of the refrigerant (Freon).It goes in the opposite direction and this is the
reverse of the cooling cycle. I stead of absorbing heat from inside the house
it absorbs heat from the air outside the house and “rejects” (or transfers)
that heat to the indoor air. Now the indoor coil has become Condenser and
the outdoor coil has become Evaporator.
Water-Source Heat Pump
refrigerant-to-air
heat exchanger
fan
expansion
device
compressor
refrigerant-to-water
heat exchanger
American Standard © 1999
reversing
valve
Spring and Fall Operation
cooling tower
off
boiler off
heat pumps in
cooling mode
American Standard © 1999
heat pumps in
heating mode
Question of the Day
• Which heat pump system is more
efficient; air-to-air heat pump or
water-source heat pump?
WSHP Configurations
unit ventilator
horizontal
vertical stack
console
vertical
American Standard © 1999
rooftop
Heat Pump Types
Cooling-Tower-and-Boiler
System
heat pumps
cooling
tower
boiler
American Standard © 1999
water pumps
Earth-Coupled System
heat
pumps
vertical-loop ground
heat exchanger
water pumps
American Standard © 1999
Vertical Loop
• Advantages
– Requires least amount of land
– Least amount of total piping
– Can require least amount of
pumping energy
• Disadvantages
– Drilling costs may be higher than
trenching costs
– Backfilling requires special material and
practices
– Potential for heat buildup
American Standard © 1999
Horizontal Loop
• Advantages
– Trenching costs are lower than
drilling costs
– May not build up as much heat
over time
• Disadvantages
– Requires more land than vertical loops
– Greater ground-temperature variations
– More total piping than vertical loops
– Risk of pipe damage during backfilling of
trenches
American Standard © 1999
Spiral Loop
• Advantages
– Requires less land area and
trenching than horizontal loops
– Lower installation cost compared
to horizontal loops
• Disadvantages
– Requires more total piping than
vertical and horizontal loops
– Still requires a large area of land
American Standard © 1999
Surface-Water System
heat
pumps
ground
heat exchanger
lake
American Standard © 1999
water pumps
Ground-Water System
heat
pumps
water pumps
well
American Standard © 1999
Benefits of a WSHP System
• Heat recovery offers energy savings
• Individual space control
• Performs both cooling and heating
• Flexibility
– Individual tenant metering
• Small amount of floor space required
• Unit failure does not affect the rest of the
system
Issues of a WSHP System
• Ventilation
• Acoustics
• Accessibility requires coordination
Single Zone System
horizontal
heat pump
return
duct
return air
grille
diffuser
American Standard © 1999
supply
duct
Single Zone Systems
Single Zone Systems
• PTAC Systems
• Split Systems
– Ductless systems
– VRF systems
• Rooftop Units
Unitary (PTAC)
• Unitary systems
– PTAC (packaged
terminal airconditioner)
PTAC (DX Packaged) Unit
PTAC Units
• Common
applications
PTAC Units
• Advantages-
Disadvantages?
PTAC Systems
• Advantages
– Very low initial
costs
– No floor space
– Easy installation
– Easy to maintain
– No ductwork
– Redundancy
• Disadvantages
– High maintenance
– Poor service life
– Poor noise
characteristics
– Low efficiency
– Need an outside
wall
– Aesthetically
challenged
Split System Cooling (DX)
1. Condenser
2. Evaporator
coil
3. Furnace
4. Filter
housing
5. Thermostat
Large DX Systems
Split System Furnaces
Split System -
w/ Gas Furnace
upflow
downflow
horizontal
Condensers
• Location issues
“Ductless Systems”
• A hybrid
PTAC/Split
system/DX
Variable Flow Refrigeration
Systems
Split Systems
• Advantages and
disadvantages of
split systems
Split Systems
• Advantages
– Can have high
efficiency
– Small floor space
– Low static pressure
– Redundancy
– Easy to maintain
and service
• Disadvantages
– Service life is
poor/average
– Noise
– Single zone
– Multiple units
creates multiple
maintenance
– Minimal fresh air
– Single zone
problems
Rooftop Units
• Self-contained packaged unit
• Heating or cooling or heating/cooling
• Can be a heat pump
Anatomy of a Packaged Rooftop
Unit
Maintenance and Operation
Issues
The dimension most often neglected
Rooftop Units
• Advantages and
disadvantages of
rooftop units?
Rooftop Systems
• Advantages
– Uses no floor space
– Low cost
– Outside air nearby
– Economizer cycles
– Easy to maintain
and service
– Large fan static
• Disadvantages
– Low/average
efficiencies
– Low service life
– Single zone
problems
– Location can make
maintenance risky
– Aesthetically
challenged