VRF Heating COP in eQUEST

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So, in the VRF interface I can enter Cooling EIR, but Heating EIR is calculated somehow from other inputs:

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The 0.3 above is actually 0.29, reflected below. But how best to get the heating EIR to 0.30, instead of 0.34? I was thinking of changing some of these "Heating Rated" temperatures. But I'd like to know if someone else has done this successfully.

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Fred Porter, LEED? AP
Principal Engineer
Sustainability Services

Porter, Fred's picture
Joined: 2015-02-03
Reputation: 0

Hi Fred,
For VRF condensing units in eQUEST, the heating EIR is a function of other variables. You can use the following keyword expression to determine the heating EIR that is used by eQUEST. It can be entered as a user input expression into one of the other keywords, so you can see how it changes when you change the other variables. (For example, you can enter it as an expression for MIN-UNLOAD-RATIO or MIN-HGB-RATIO, which have default values that are close to the heating EIR, in case you leave the expression in when you simulate.) You can see all the variables that determine the heating EIR in the expression:

/* This expression will calculate the heating EIR that DOE-2.3 will use
for a VRF condensing unit. You can input this as a user expression
in another keyword such as MIN-UNLOAD-RATIO. */


Remember that fan energy should be accounted for when converting rated EER or COP to EIR. Doug Maddox shows how to calculate VRF EIR in this presentation:
Cooling EIR for the condensing unit: (3.413/AHRI_EER-0.01138)/(1+0.01138)
I believe you would reverse the fan energy for heating. Heating EIR = (1/COP+0.01138)/(1-0.01138)
The constant 0.01138 is the allowance for indoor fan EIR.
Also, I created a modified BDLDialogs.txt file to use with DOE2.3. The file adds these keyword capabilities to the eQUEST interface:

* SYSTEM:LOW-FAN-PWR (for PVVT systems)
* CONDENSING-UNIT:TYP-CAP/SYSTEM (for VRF condensing units)
The file also adjusts the number of decimal places displayed for several keywords, such as the cooling EIR that you mentioned. I am happy to share this file with eQUEST users (it is ~1.7 MB).

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer

[Pathfinder-EA-logo-2]T: (585) 698-1956 F: (585) 325-6005
bbishop at pathfinder-ea.com www.pathfinder-ea.com
134 South Fitzhugh Street
Rochester, NY 14608 [cid:image007.png at 01D51B76.269AD5B0] Ask me why Carbon Fee & Dividend may be right for you.

Bill Bishop's picture
Joined: 2012-02-25
Reputation: 7

Bill, thanks,
So what you?re saying is that if I want to change the ratio between cooling and heating design EIRs, I need to create custom curve coefficients. Actually, no! Just like there is only one ?EIR? input, the same curves are used for heating and cooling, based on refrigerant ?lift.? So the reason the heating EIR listed is always lower than cooling, is that the heating rated lift (SDT-SST), is 86F, and the cooling lift is 80F.

I briefly tried changing these ?HEAT-RATED-SST/SDT? #s but that did not produce the expected results.

MAYBE the program is actually DOING the right thing; it?s not clear how these eQUEST EIRs account for compressor heat; probably they don?t. The formulation you?ve provided does not; it treats heating and cooling the same. BUT when rated for heating, the compressor heat is useful, and accounted for in AHRI COP ratings, compared to the eQ reported/calculated heating EIR. Because I still have some faith in JJH?s ability to provide reasonable representations of mechanical equipment, as opposed to that newer guv?mint software, I?ll bet that heat is just accounted for ?separately.? Off to the hourly reports. Still better than wallowing in ?sql? files from that other software.

OK. Ran the hourly reports. It looks like what I wrote above is about it.


Porter, Fred's picture
Joined: 2015-02-03
Reputation: 0