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Coil:Heating:DX:MultiSpeed - rated waste heat fraction of power input

Hi,

I'm trying to setup an idf file with a Coil:Heating:DX:Multispeed object. I've read the engineering manual and the input-output manual and I still can't figure this out.

What is the waste heat fraction? I set this to 0.0 and I get an error:

* Severe * <root>[Coil:Heating:DX:MultiSpeed][Heat Pump DX Heating Coil][speed_1_rated_waste_heat_fraction_of_power_input] - "0.000000" - Expected number greater than 0.000000

I don't know why I need to have a waste heat component in the heating component of a heat pump.

Could someone help me understand what this value does?

Thanks

Sebastien Brideau's avatar
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Sebastien Brideau
asked 2024-01-03 16:31:02 -0500
Aaron Boranian's avatar
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Aaron Boranian
updated 2024-01-04 10:21:52 -0500
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1 Answer

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Coil:Heating:DX:MultiSpeed

The rated waste heat fraction is needed to calculate how much waste heat is available at the rated conditions. In addition, up to 6 modifier curves are required per speed.

6. The waste heat modifier curve (function of temperature) is a bi-quadratic curve with two independent variables: outdoor air dry-bulb temperature and the heating coil entering air dry-bulb temperature. The output of this curve is multiplied by the heating input energy, the waste heat fraction of heat input to give the recoverable waste heat.

Field: Speed <x> Waste Heat Function of Temperature Curve Name

The name of a bi-quadratic performance curve (ref: Performance Curves) that parameterizes the variation of the waste heat recovery as a function of outdoor dry-bulb temperature and the entering coil dry-bulb temperature for Speed <x>. The output of this curve is multiplied by the rated recoverable waste heat at specific temperature operating conditions (i.e., at temperatures different from the rating point). The curve is normalized to a value of 1.0 at the rating point. When the fuel type is electricity, the field is either left blank or ignored by the program. When the fuel type is not electricity and the parent object AirLoopHVAC:UnitaryHeatPump:AirToAir:MultiSpeed does not require waste heat calculations, this field is ignored. If the field is blank, a warning will be issued and simulation continues. When the fuel type is not electricity and the parent object AirLoopHVAC:UnitaryHeatPump:AirToAir:MultiSpeed requires waste heat calculations, if this field is left blank, the program assumes a constant value of 1 to make simulation continue and a warning will be issued.

Field: Fuel Type

This alpha field determines the type of fuel that the chiller this coil uses. This field has seven choices: Electricity, NaturalGas, Propane, Coal, Diesel, Gasoline, FuelOilNo1, FuelOilNo2, OtherFuel1 and OtherFuel2. This is a required field with no default.

(I think "the chiller" above is wrong. It should be "this coil".)

Is the above description in Input/Output Reference insufficient for you?

Waste Heat Fraction is irrelevant if you use electricity for the energy source of the compressor, but you need to input a value greater than 0 as the severe error suggests.

A typical fuel type other than electricity would be Natural Gas, as used in gas heat pumps (absorption heat pumps).

Keigo's avatar
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Keigo
answered 2024-01-04 00:17:08 -0500
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Hi Keigo,

What confused me was that I assumed that since I used electrical as a fuel, I thought the waste heat fraction would just be ignored completely. So what I understand now is that I must enter a value greater than 0 and EnergyPlus will ignore it in its calculations. This is very helpful.

Thanks you very much for your help. I really appreciate it.

Sebastien Brideau's avatar Sebastien Brideau (2024-01-04 08:11:13 -0500) edit
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