Thermostatic Mixing Valve install — circulation loop?
Hello,
I am new to using the forum, I have searched for this issue but not found much, forgive me if I overlooked something. Our family of 4 lives in a passive solar 80o sq ft house in Maine with PV/heat pumps and wood stove. When I built the house I installed an AO Smith 50 gallon hybrid heat pump water heat and we find that if we leave it in the most efficient mode we run out of hot water pretty quick between me and the 3 females I cohabitate with. This is despite me installing a 1/1.5GPM shower head. They love their baths.
I want to add a thermostatic mixing valve, set it at 120, and increase our water heat tank temperature to 150 to extend the time we have usable hot water at our fixtures. I want to keep the hot water heater in heat pump mode to save energy and because I grow Cannabis in our basement the dehumidifying effect is helpful. Is it recommended that I install a recirculating loop with pump? Or can I just install the valve right near the water heater and use the tempered water to feed my whole house?
I am thinking of getting this valve, Made in USA, unless someone recommends another: https://www.supplyhouse.com/Apollo-Valves-34ALF214S-3-4-Sweat-Thermostatic-Mixing-Valve-Lead-Free
Thank you for your help!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Recirculating is only used when there is a need for instantanious hot water. The pump uses energy and the process cools the hot water. Necessary no, personnel choice only. I turned my recirculated off.
150 sounds awfully hot for a heat pump water heater. Heat pumps are less efficient the greater the temperature difference between the heating stage an the cooling stage. If the heat pump can even get that hot it's going to be inefficient, perhaps less efficient than a resistance tank.
Consider putting a loop around the wood stove and pump water thru the loop that would heat a second tank.
Walta
Thank you all for your replies! Based on what DCContrarian wrote, I am not likely not gaining any efficiency by installing a thermostatic mixing valve and running water heater in heat pump mode over simply switching the water heater to full electric resistance mode in the winter. That meets our needs. Sometimes the best answer is to do nothing and not over complicate it!
Interesting post, my garage door gets well over 100 F on a sunny day with outdoor temps in the 20sF. I noticed this article on combining solar and heat pump in cold climates: https://www.phcppros.com/articles/10966-solar-thermal-and-heat-pump-hot-water-hybrid
Since it sounds like the heat pump only mode will not meet your demand and the electric mode cost more than you would like to spend you may want to conceder trying the hybrid mode is sort of half way in between mode.
Do you have room for a second tank?
Walta
If you put a regular resistance tank downstream of the heat pump and set its thermostat slightly lower, it will only run when the HP can't keep up and for standby losses. Kind of a roll-your-own hybrid.