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Q-Pump - Non-Reversing Heat Pump |
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Thank you for responding to our Q-Pump
ad that appeared in Engineered Systems. We're happy to know that
you're interested in Desert Aire's innovative heat pump technology.
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The Benefits of Desert Aire’s Q-Pump
In the ad you just read, we provided five distinct benefits stating why our Q-Pump
non-reversing technology is superior to reversing heat pumps. Below
you’ll find information and diagrams which fully explain each benefit.
• Avoids inefficiencies of high pressure on compressors when 2-element systems reverse to cooling
A
refrigerant design that requires coils to work bi-directionally must
accept significant performance degradation in order to operate in all
modes under all ambient conditions.
For
example, a typical air-side coil functioning as a condenser must pass
the majority of the refrigerant through its tubes either as a
superheated vapor or a low quality liquid/vapor mixture. The flow of
this mixture must be at a sufficient velocity to “sweep” refrigeration
oil back to the compressor to ensure proper lubrication.
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the system reverses so that the coil now becomes an evaporator, the
refrigerant’s pressure drop within the coil becomes much higher. This
occurs because the majority of the refrigerant passing through its
tubes now exists as a sub-cooled liquid or high quality liquid/vapor
mixture. |
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The
resulting high evaporator pressure unfortunately reduces the cooling
capacity of a heat pump because it forces the compressor to labor in
order to overcome the friction between the liquid refrigerant and the
tube walls of the evaporator coil. While a coil can be designed to
reduce refrigerant pressure losses when it functions as an evaporator,
this same coil will unlikely be a good condenser. The velocity of its
refrigerant will most likely be insufficient to sweep lubricating oil
back to the compressor.
Desert Aire’s 4-element Q-Pump
is a non-reversing heat pump. It does not force a coil to act as both
a condenser and an evaporator. This avoids burdening the compressor
with high pressures, therefore allowing the system to function more
efficiently in the cooling mode.
• No reversing valve allows for quick, easy transition between winter and summer modes.
One of the key innovations of our Q-Pump
is that it is a 4-element, non-reversing heat pump and therefore
requires no reversing valve. As cited in the previous bullet, problems
arise when 2-element heat pumps switch from heating to cooling and vice
versa. Specifically, refrigerant velocity is reduced so that it isn’t
capable of sweeping lubricating oil back to the compressor.
Because refrigerant never reverses direction in our Q-Pump, it can seamlessly switch from the heating and cooling modes without ever losing control of LAT.
• Less potential for slugging and flashing compared to 2-element systems.
This additional side benefit follows as a direct result from Q-Pump’s non-reversing design.
A 2-element system requires a reversing valve. As refrigerant switches
directions with the change of seasons, it has a difficult time of
sweeping lubricating oil back to the compressor. This inhibited flow
of the refrigerant increases the chances of slugging and flashing in a
traditional 2-element heat pump.
Our Q-Pump
does not use a reversing valve and therefore refrigerant never changes
direction. This reduces the possibility of slugging and flashing.
• Water chiller used as an evaporator in the water loop helps achieve COPs of 6+
Our Q-Pump
is a 4-element, water source heat pump. This system uses one air
condenser and one air evaporator, each component devoted to perform its
function as designed. These coils make up the first two elements of
our Q-pump.
The other two elements consist of a water chiller and a water condenser in the water loop.
The water condenser is used for the balance of the heat of rejection in the cooling mode.
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Q-PumpTM Schematic with SAT Control: Cooling Mode
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the water condenser continues to act as a heat sink to the water loop
in the reverse cycle, the water chiller is also activated as an
evaporator in the heating mode. |
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| Q-PumpTM Schematic with SAT Control: Heating Mode |
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It
is in the heating mode that the water chiller can take advantage of
extracting the very heat of rejection which is initially “deposited”
into the water loop by the water condenser. This boosts the
temperature of the refrigerant to improve the efficiency of the
compressor further down the line in the refrigerant loop. By
recovering this energy, a basic Q-Pump
system is capable of heating 100% outdoor winter air, down 15° F,
without the need for auxiliary heat. When incorporating an enthalpy
wheel with a TotalAire DOAS Q-Pump, the system can achieve the same results, but with even colder 100% outdoor air down to -10° F.
Also, the recovery of the heat of rejection has minimal impact on the
water temperature allowing a great deal of energy to remain in the
water for other mechanical equipment incorporated into the loop.
The function of this entire design is what makes Q-Pump so efficient, enabling this system to achieve EERs of 14+ and COPs of 6 or greater!
• Q-Pump DOAS units control LAT to ±2.0° F in heating and cooling
Using our Q-Pump
with either our TotalAire or VerticalAire DOAS units gives you the full
benefit of complete control over the heating and cooling of your
facility.
Desert Aire’s DOAS equipment provides precise
discharge temperature by using fully modulating hot gas control valves
and proper refrigerant management. Other systems that use solenoid
valves and/or liquid sub-cooling loops can control the leaving air
temperature to only ±10° F and typically are closer to ±20° F.
In addition, these systems do not comply with ASHRAE Standard 90.1.
They require new energy to trim the leaving air temperature to avoid
overcooling of the space. The accuracy of the system also directly
affects the cost of operation. Costs rise when new energy is required
to adjust high temperature fluctuations in order to meet preset
temperatures. The table below shows the potential increase in energy
consumption that can occur at different control accuracies.
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| To view "Technical Bulletin 21 - Heat Pump Design for 100% Outdoor Aire Systems," please click here. |
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To view a TotalAireTM Brochure, please click here.
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| To view a VerticalAireTM Brochure, please click here. |
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Find a Desert Aire Sales Representative Nearest You
If you're interested in locating and contacting your local Desert Aire sales representative, click here.
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International Sales Assistance
If you would like to find a Desert Aire representative and are outside
the United States and Canada, or have any other questions regarding
Desert Aire, please e-mail:
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encourage all engineers to become registered users on our website. As
a registered user, you can access additional information such as unit
dimensional sheets to help you size your application. You're also able
to order hard copies of Desert Aire's literature as a registered
engineer.
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