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# How do coil frost/freeze warnings influence the total energy performance of the HVAC system?

I run my models with the E+ HVAC Template HVACTemplate:System:UnitaryHeatPump:AirToAir and it shows many warnings of possible coil frost/freeze. What can I do to avoid this? I am not an HVAC engineer that's the reason why I am using a template.

I am wondering if these warnings are influencing the total energy performance of the model? I am simulating different passive design and comparing their HVAC consumption.

* Warning * CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed "ROOMWEST AIRTOAIR HEATPUMP COOLING COIL" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = 0.49 C. * ~~~ * ...Occurrence info = DOUBLE COTTAGE, 01/02 12:00 - 12:01 * ~~~ * ... Possible reasons for low outlet air dry-bulb temperatures are: This DX coil * ~~~ * 1) may have a low inlet air dry-bulb temperature. Inlet air temperature = 23.699 C.
* ~~~ * 2) may have a low air flow rate per watt of cooling capacity. Check inputs. * ~~~
*
3) is used as part of a HX assisted cooling coil which uses a high sensible effectiveness. Check inputs. .... *** ===== Recurring Error Summary =====
*** The following recurring error messages occurred.
*** *** * Warning * CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed="ROOMWEST AIRTOAIR HEATPUMP COOLING COIL" - Full load outlet temperature indicates a possibility of frost/freeze error continues. Outlet air temperature statistics follow: *** * ~~~ * This error occurred 1903 total times; *** * ~~~ * during Warmup 0 times;
*** * ~~~ * during Sizing 0 times. *** *
~~~ *
Max=1.998861 Min=-2.133559

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@Xandrika I changed your air-to-air-heat-pump tag to the more generic air-source-heat-pump.

( 2015-07-13 08:07:51 -0500 )edit

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This is not an area I can speak to with authority, but considering nobody has responded I'll put in my two cents, especially since this is an extremely common warning and most of us have trained ourselves to ignore it for better or worse.

• Cooling during periods of time when it is cold outside is very possible in load dominated commercial buildings. Don't think just because your cooling coil is on when it is cold outside means something is wrong with your control.
• You might consider using an economizer to keep the coil from running during some of these hours.
• Real coils might have mechanisms to prevent coil freezing (reverse cycle or resistance heating), CoilCoolingDXSingleSpeed is not capturing this so you might be underestimating energy consumption a little.
• At the extreme you might be dropping off the valid range of the coil performance map. Perhaps overestimating energy consumption of the vapor compression cycle a little.
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@Kyle Benne, thanks a lot for your comment.

( 2015-07-14 05:55:43 -0500 )edit