I just installed a heat pump water heater (Ruud/Rheem) in my crawlspace. It is soon to be hooked up to a 50 gallon buffer tank and DSH Question is, manufacturers quote COPs of 2.0 or so for these, but I assume this is for summer when it is quite warm (or a hot garage) but my crawl space this time of year is around 50-55dF and will get a big cooler as winter progresses. Anyone seen charts or information regarding COP at different ambient temps? AKA at what temperature does the 'eco' or all heat pump setting become less effective than the regular setting? AKA when does COP of the heat pump approach 1.0?

Water Heaters are rated by EF, Energy Factor, not COP. EF accounts for cyclic and standby losses. EF for an HPWH falls off gradually until ambient is cool enough such that the unit begins to ice up during operation; then it plummets. I'd expect that to occur in the 45-50*F range. EF should still exceed the 0.9 range typical of resistance electric units even with some icing.

Possibly contrary to your intuition, as DSH contribution rises, the EF of a downstream HPWH drops. This happens for two reasons - 1)With good DSH performance, HPWH is reduced to short cycling to overcome standby losses. EF drops with shorter cycles. 2) EF also drops with warmer incoming water. A resistance heating element has the same efficiency regardless of water temperature, but an HPWH draws more power and transfers less heat as incoming water temperature increases. My Geyser starts a cycle at 500 Watts or less, but ends a cycle at 750 Watts when inlet and outlet water are at their warmest. In high summer when DSH tank is running around 110 degrees the EF is not much better than 1.0, but the cooling and dehumidifying is still a worthwhile bonus.

Understand that my remarks on icing and EF are educated guesses - I don't have hard data on a Ruud / Rheem operating in a 50 degree crawl space - we don't have those in Florida.

Thanks. Makes sense. I already have a WelServer sitting here, but I haven't decided how I am going to hook up the power monitoring yet. I would like a Watt-node, but haven't decided if/when/how I am going to set that up.... I honestly don't know what Watt-Node to order (anyone help?) to monitor the HPWH and Climatemaster...

I'm a couple weeks into testing a TED 5000 system for eventual use in home energy audits. There were some growing pains, but I've worked through those and have to say that the TED 5000 system works well. Put one MTU on the whole house conductors and one or two more on loads of particular interest.

Depending on the nature of the crawl and your geographic location, I'm not crazy about this design.
If a crawl weren't conditioned I wouldn't duplicate this install in MI.
Joe

Crawl space isn't conditioned, but it is quite large volume wise. My house is 4800 sq ft, 2/3 of that on one level with a partial basement. Total length of the house is 100ft. So the crawl space averages about 3 ft tall, 20 ft wide x 42 ft long, with the area where the equipment is being 7ft tall x 7ft wide x 20 ft wide. Total cubic volume of 3ft area is at least 2500 cuft and the tall area is 980 cuft so I am drawing from an area of 3500 or so cuft for the heat pump water heater (versus required minimum of 1000 cuft). I'm in central Washington state, so we are much more mild in the winter than Michigan. Typical winter lows are low 20s and most winter days are over freezing with only a small part of winter where the daytime highs are less than 30 and many are 40dF or so. Clearly, part of the winter the EF will be 1.0 or so, but then it isn't any worse than a straight electric. During the summer the EF will likely be much better, plus it will cool the crawlspace (and thus, slightly help cool the house) We'll see....I'm unimpressed with its recovery time thusfar, kind of wish I had gone with the AO Smith Vertex gas instead...