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EnergyPlus packaged heat pumps energy meter difference from the coil to energy balance

asked 2022-03-10 00:52:47 -0500

sajithwjay's avatar

updated 2022-03-10 15:46:47 -0500

I am implementing the packaged heat pump model in EnergyPlus and I notice that for heating (and cooling also) there is a difference between the metered value of HeatingCoils:EnergyTransfer [J] value and Heating:EnergyTransfer [J] value (this is for the entire building). In fact Heating:EnergyTransfer [J] value is lower than the HeatingCoils:EnergyTransfer [J] value. If you could point out the reason for the above reduction I would be grateful. The building I am modelling is the MidRise Building of the prototype commercial buildings database.

Related EnergyPlus example file: PackagedTerminalHeatPump shows the same characteristic

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answered 2022-03-10 16:31:50 -0500

updated 2022-03-12 16:47:26 -0500

Look in the mtd file and find the meters in question. That file will show you what is on each meter. The Heating:EnergyTransfer meter is, if I recall correctly, a sensible only meter. The HeatingCoils:EnergyTransfer is likely total energy transfer, including latent. This would explain why the heating coil energy transfer is larger than heating energy transfer. In fact I just went through this for AHSRAE Std 140 where the html District Heating energy was larger than the Heating:EnergyTransfer and I was confused, until I realized the difference between a meter including latent heat and one that does not.

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Thank you very much for this quick response. I also noted that when looking at the "Zone Air Heat Balance:System Air Transfer Rate" for the heat pump the contribution to the heat balance actually sums up to "Heating:EnergyTransfer" value rather than the "HeatingCoils:EnergyTransfer ". Does this mean the latent part does not contribute to the zone heat balance?

sajithwjay's avatar sajithwjay  ( 2022-03-10 16:57:34 -0500 )edit

At the zone level heating is a sensible only heat transfer so the latent component is not included. At the coil model, the heating is usually total heat transfer and would include fan heat and outdoor air when necessary. So these 2 are very different depending on the simulation model. Latent contributes to the zone heat balance with respect to zone conditions, whether or not the latent is included in the energy tranfer meter or report. When you see "Zone" in a report variable, think supply air entering the zone wrt the zone conditions. And if heating, then sensible only is typical (MdotCpDt).

rraustad's avatar rraustad  ( 2022-03-10 17:54:22 -0500 )edit

"At the zone level heating is a sensible only heat transfer so the latent component is not included." Well it really depends on the report variable in question, whether it is sensible heat transfer or total heat transfer. You have to review what the report variable represents to know if latent is included (i.e., sensible or total heat transfer).

rraustad's avatar rraustad  ( 2022-03-10 17:56:12 -0500 )edit

Thank you for the further pointers. I verified that your explanation is correct for the heat pump cooling. The sensible portion is used for the heat balance. The concern is where there is a difference for the heating pump heating operation as well. This cant be explained from the above explanation (thought process) because the latent component for the heating operation is really small.

sajithwjay's avatar sajithwjay  ( 2022-03-11 17:28:30 -0500 )edit

Since I don't see a meter that could be used to figure this out, if you look at the zone inlet node Mdot * deltaH (use Output:Variable,your node name,System Node Mass Flow Rate,hourly; and Output:Variable,your node name,System Node Enthalpy,hourly;) you should see where the difference is. It's probably a difference of latent between these 2 meters.

rraustad's avatar rraustad  ( 2022-03-12 22:36:33 -0500 )edit

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Asked: 2022-03-10 00:52:47 -0500

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Last updated: Mar 12