5 ms·
A conventional heater can, at best, use 100% of the energy to heat both the water and the house. A heat pump would use some of that energy to capture some more
by MayeulC 6y ago
A conventional heater can, at best, use 100% of the energy to heat both the water and the house.
A heat pump would use some of that energy to capture some more from a heat source (outside air, or geothermal, ground temperature). It gets less efficient as the heat source becomes cooler, so it might not be such a good idea in very cold climates. Theoretically, though, it shouldn't get lower than 100%, and efficiencies can reach 300% pretty easily.
I haven't done an extensive search on the topic, here is one of the first sources I found with the kind of graph I wanted: https://www.nordicghp.com/2017/01/heat-pump-effective-temperature-range/ https://www.nordicghp.com/2017/01/heat-pump-effective-temper...
I read about 270% at -4°C (25°F). 1 watt of electricity in, 2.7 watts of heat out, not bad. The same graph reads about 480% at 18°C(65°F), and 150% at -20°C (-5°F). I know that gas heat pumps exist as well, and some systems are hybrid, so it sounds like a no brainer to me. On the flip side, they can be quite expensive, so do your calculations relative to the temperature history, and hourly electricity hours. It would be more efficient to heat when the air is warmer during the day (assuming air pump), and combine that with a well-insulated house.
Solar (thermal or electric) is pretty interesting too, I wonder what kind of efficiency one can get with photovoltaic + heat pump (photovoltaic is more versatile, being more useful during summer).
- semi-extrinsic 6y agoI think GP is talking about heat pump water heaters that are working between the air in the room where heater is installed and the hot water. Very different from what you are suggesting. It could still make sense if it is installed in a room with lots of waste heat, e.g. next to a clothes dryer and other appliances.
- war1025 6y ago> I think GP is talking about heat pump water heaters that are working between the air in the room where heater is installed and the hot water. Correct. Every heat pump water heater I've ever seen has the heat pump directly on top of the water tank. It's possible they make ones that tie into an external heat pump, but I've never seen one.
- fomine3 6y agoIn Japan, separated heat pump unit / tank is pretty ubiquitous and never seen union unit. https://echonet.jp/introduce_en/gz-000505/ https://echonet.jp/introduce_en/gz-000505/
- MayeulC 6y agoHuh? That would indeed be pretty dumb. I would have at least expected a duct that pumps air from outside... Heat pumps make little sense if you don't have access to a thermostatic source, or indeed any "free" heat source.
- war1025 6y agoThe trouble with water heaters is you want hot water year round. Heat pumps are pretty ineffective once you get down close to freezing. So having an exterior air source heat pump would only make sense for maybe half the year in a lot of locations. Generally utility rooms in houses have a decent amount of waste heat anyway from being near the furnace, so it probably does work out decently a lot of the time. My in-laws have a heat pump water heater and it makes their basement noticeably colder in the summer, which is pretty nice.
- choeger 6y agoErr, what? The heat exchanger has to be outside the house of course! Who would even build that inside? That's crazy!
- semi-extrinsic 6y agoTo counter that point, high-end tumble dryers are universally built with a heat pump that is all located inside the same room (it's even in the same device). It's because they are cooling air to dehumidify it (the drying part), then they pump the heat back into the same air to circulate back into the wet clothes. https://images.jifo.co/10180236_1567417620885.png https://images.jifo.co/10180236_1567417620885.png