You are correct on all counts. And so purchasers of HP water heating should consider their situation.
If the HP water heater is in your basement and you already run a de-humidifier, then the Hot water from a HP water heater is virtually free. Because the cold side of the coils will condense the humidity out of the basement and you can stop burning all that energy in a dehumidifier. If your heatpump water heater is in a room in the conditionemd part of the house and you live in Florida, then again, it is almost free because the cold side of the water heater is cooling the house. The worst case would be a HP water heater inside a conditioned space in the north where you are dumping cool that you don't really want a good portion of the year. Or you can add louvers and doors to manage the heat or cool as the seasons change. Put it outside in a closet with a south facing wall of glass windows. Then the sun provides the heat. Oh, and my unfinished basement has never changed temperature that we can tell. It is 60F in the summer, 60F in the winter. I think of the HP water heater in the basement as a "geothermal" heatpump because no matter how much heat it draws from the basement, all that is being replenished by the 1500 sQft of surrounding floor and dirt at 60F. Now I am sure it is not really 60.0F all the time, but we just do not notice any change season to season not worth putting a themrmoeter down there to worry about. Bob -----Original Message----- From: EV <[email protected]> On Behalf Of Peri Hartman via EV Sent: Thursday, July 18, 2019 5:04 PM To: Electric Vehicle Discussion List <[email protected]> Cc: Peri Hartman <[email protected]> Subject: Re: [EVDL] Solar off grid with an EV? (DC AC/heatpumps and waterheating) (Really off topic, here) I'm curious about the overall efficiency of heat pump HW heaters. If it's in your garage (or basement), and it's drawing heat from the garage, that's going to create a very cold garage, right ? Further, if adjoining spaces or spaces above aren't fully insulated from the garage, you'll also be increasing the heat load in those spaces. All this would seem to reduce the efficiency of the HW heater dramatically. So, shouldn't the heat pump be vented to the outdoors ? If so, then its efficiency would be determined by the climate where you live. In winter it may rely solely on resistance heating. Though it should do quite well in summer in most parts of the US. Peri ------ Original Message ------ From: "Robert Bruninga via EV" <[email protected]> To: "Electric Vehicle Discussion List" <[email protected]> Cc: "Robert Bruninga" <[email protected]> Sent: 18-Jul-19 1:23:02 PM Subject: Re: [EVDL] Solar off grid with an EV? (DC AC/heatpumps and waterheating) >> *-Because a heat pump system is using energy to "move" existing >> heat, it gives you 400% (or more!) efficiencies. [i.e. you use 800 >> watts to drive a compressor and fans, but get 3,200 watts of heat >> into the tank, while cooling the area around the water heater.] > >I think it is more like 3 to one. The higher temp you want the water, >the lower the efficiency and can range between 2 to 1 or 4 to 1. > >> I haven't shopped for heat pump water heaters. It looks like I should. >> I have recently resolved to stop using my propane water heater... > >Here is my summary. They are often called HYBRID water heaters with >the heatpump heating the incoming water at the bottom of the tank and >then (if >enabled) a resistance element at the top to provide rapid response and >higher temperatures. Remember the heatpump is the most efficient when >it is throwing energy at the incoming 60F water with a greater delta-T > >The efficiency goes down as the temperature rises. SO I have mine set >to heat the bottom of the tank to only 105F (where it is still pretty >efficient) and then the top coil heats the rest to 115F. > >IN fact, I really have the Heatpump one in series with the old pure >electric one and both have an added 4" insulation around them. So I >let the heatpump one heat its entire tank to 105F, from there it goes >into the old heater which has the bottom element turned off and the top >element set to 115F. SO the bulk of the heating (55 to 105F (50 >degrees) is done at >3:1 electric effdiciency, and the final 105-115 (10 degrees) is >straight electric at 1:1 (but saves wear and tear on the heatpump, >working much harder j ust to get the final 10 degrees). > >Remember you can drastically change the "capacity" of a water heater >simply by the temperature setting. If you set it to 140F, then when >you take a shower, you only use a little bit of hot water mixed with >more cold water to get to final temp. This gives you a lot of "hot" water capacity. > >If you don't use that much hot water, then set the temperature to 110F, >but now then your shower will be using mostly hot water from the tank >and only using a little bit of cold water. Now your capacity is much >less but you save energy by not throwing a higher temperature away >mixing it all with cold water. > >Your wife may vary. > >Bob >http://aprs.org/Energy-Choices.html >_______________________________________________ >UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >http://lists.evdl.org/listinfo.cgi/ev-evdl.org >Please discuss EV drag racing at NEDRA >(http://groups.yahoo.com/group/NEDRA) > _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
