Chiltrix CX34-4, Installation And Operation Manual

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Chiltrix Inc. www.chiltrix.com
Dynamic Outdoor Reset Control
The Chiltrix CX34-4 unit is equipped with an automatic outdoor reset function that can be accessed via the
onboard controller.
Advantages & Misconceptions of Using Outdoor Reset
Most people in the radiant heating industry will tell you that outdoor reset is used to get more BTU delivery
from the radiant system on a day when the radiant system can't deliver enough BTUs to keep up with the
load, and they use outdoor reset to crank up the radiant heat operating temperature to 120F, or higher.
While that's true, it's also true that the best designed air to water radiant systems will be able to deliver
what's needed at a fairly low temperature even with severe outdoor design conditions.
So if you can't get enough radiant capacity into the floor, then if possible, add some to the walls or ceiling.
Note that radiant heat works just as well from the ceiling or walls as it does from a floor. And in some cases,
it works better from the ceiling.
Why does keeping the operating temperature low matter so much?
With a fossil fuel burning boiler, it doesn't matter. Gas, propane, and oil efficiency does not vary with
outdoor temperature. But that's not the case with a heat pump.
Here's why:
For a real-world example, at 0F outdoor temperature, an air to water heat pump such as the CX34 will have
>20% higher capacity when used with an operating temperature of 95F compared to operating at 122F. And
COP at 95F will be >30% higher at 95F than at 122F.
So why use outdoor reset?
You can use reset when it is simply not possible to design the indoor side of a system to handle the peak
BTU load using a low operating temperature.
But the best use of reset is as a strategy for extra energy
savings , by designing the indoor side of the system to handle the peak load at the lowest possible operating
temperature, and then letting the system automatically reset to an even lower and even more efficient
temperature at times when weather is milder!
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