Hi Everyone,
I've come to the belated realization that I've been using one set of performance curves to describe equipment rated at two very different conditions. I use PVVT systems to model both water-loop heat pumps and ground-source heat pumps, and I've been using the family of performance curves that start with "GSHP/WLHP" for both system types. (These curves are in the "GSHP/WLHP curves" section of the library, and they're the default curves when you specify a PVVT system with a water-cooled condenser.) The name would seem to imply that these curves are valid for both GSHP and WLHP systems, but I had occasion to graph them recently and found that they're normalized to the ISO rating conditions for a ground-source heat pump - an entering water temperature of 32F and an entering air dry bulb of 68F. (I presume the same issue exists for cooling, but for brevity's sake I'll restrict this to heating.) Entering the COP for a heat pump rated at the much higher WLHP rating temperature (68F water) would overpredict performance by a lot.
Does anyone have suggestions for performance curves (eQuest library or otherwise) that are appropriate for a water-loop heat pump? I found some curves labeled "Water-Loop HP" in the eQuest library that seem to fit the bill, since they come to unity at an entering water temperature of 68F and an entering dry bulb of 70. Turns out these are the defaults if you select a Water Loop HP air-side system, which I've never done before because my usual M.O. is to start with PVVT. The library curves in question are:
GSHP/WLHP_Heat_Cap_fEwbEwt
GSHP/WLHP_Heat_EIR_fEwbEwt
HP-Heat-Cap-fEDB&EWT
HP-Heat-EIR-fEDB&EWT
A small, very nitpicky aside: The ISO ratings actually specify an entering air dry-bulb temperature of 68F, but the eQuest library curves seem to come to unity closer to 70. Far from a big deal in the grand scheme of things, just the scuff on your shoe you keep trying to ignore.
Drew Morrison
Energy Engineer
he/him/his
608.210.7151
dmorrison at slipstreaminc.org
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