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diy solar

Need some suggestions...HVAC/heat pump, heat strips & solar

mcdonsco

New Member
Joined
Jan 26, 2024
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4
Location
Portland Oregon
I'm setting up an EcoFlow delta pro ultra system and Renogy panels (8kw array, starting with 2 ultras so 12kwh until we can see what the energy needs are after replacing our 38 year old heat pump that we definitely could not power with this system (nor our previous generator).

I've basically sized the system for once we have the heat pump replaced.

But, I've run into an issue with the heat strips needing 100amp service. We're likely going with the New Bosch inverter systems, specifically M18 or M20 3 ton. They're rated down to 5° & -4° respectively and in our area, we never get into single digits so technically we wouldn't use nor need the 15kw heat strips that these systems require (though we often used the ones in our old HP now as we had to when it got to freezing or below), but my understanding is, if these can operate down to those rates lows, we wouldn't need nor would never use the heat strips?

I've been talking to installers about maybe having the heat strips only on grid from our panel, then run everything else through the smart panel 2's (2 of them) / Ultra's and if/when the system wants to turn the strips on, it can and won't touch solar / battery power. But, will the rest of the system still work? If grid goes down (and thus strips are down) aside from blowing cold now and then for defrost, should the system still heat/work?

Basically, I have a bit of a cluster F and I'm not sure how to resolve this.

Any/all suggestions would be helpful. We haven't settled on an HVAC installer yet, for a few bids and now it seems like I may have to go with whoever can help me make this work?
 
It should work the way you've described, although heat strips turn on whenever the thermostat says to turn on auxiliary heating. I JUST ran into this - I had to add a second 18kpv inverter because when it got cold enough that the heat pump couldn't keep up, the thermostat would kick in the heat strips, and the single inverter would overload 😕. I learned it by upping the temp by 3 degrees to kick on the system while it was cold out. Whenever the thermostat says there's a high demand for heat, the aux heating seems to come on. I don't know if there are smarter thermostats that you can control this better or not, but this was my experience in the last two weeks when it got down to 15deg here.

I have a 4 ton trane heat pump fwiw
 
Did anyone run a heating load calculation? That would determine what equipment is appropriate.
As far as controlling it a good tech should be able to work with the electrician to do what you want. A good control electrician can likely figure it out also.
 
Wouldn't it be simpler to look into a mini-split or HP that doesn't require heat strips? We live in Maine, have Emporia Vue devices in each building with a mini-split, and have two Daikin mini-splits and a Mitsubishi (with hyper heat) and I've never seen them consume enough power to be using resistive heat (i.e., heat strips). I've run these units at -14F! We had an ancient HP (ducted system) in our previous home in PA and the heat strips would come on when temps were in the teens (maybe 20s) but not these units. Perhaps it's different for ducted units, but I don't think we even have heat strips in our mini-splits, and if they were required anywhere, we'd be a top contender.
 
I'm setting up an EcoFlow delta pro ultra system and Renogy panels (8kw array, starting with 2 ultras so 12kwh until we can see what the energy needs are after replacing our 38 year old heat pump that we definitely could not power with this system (nor our previous generator).

I've basically sized the system for once we have the heat pump replaced.

But, I've run into an issue with the heat strips needing 100amp service. We're likely going with the New Bosch inverter systems, specifically M18 or M20 3 ton. They're rated down to 5° & -4° respectively and in our area, we never get into single digits so technically we wouldn't use nor need the 15kw heat strips that these systems require (though we often used the ones in our old HP now as we had to when it got to freezing or below), but my understanding is, if these can operate down to those rates lows, we wouldn't need nor would never use the heat strips?

I've been talking to installers about maybe having the heat strips only on grid from our panel, then run everything else through the smart panel 2's (2 of them) / Ultra's and if/when the system wants to turn the strips on, it can and won't touch solar / battery power. But, will the rest of the system still work? If grid goes down (and thus strips are down) aside from blowing cold now and then for defrost, should the system still heat/work?

Basically, I have a bit of a cluster F and I'm not sure how to resolve this.

Any/all suggestions would be helpful. We haven't settled on an HVAC installer yet, for a few bids and now it seems like I may have to go with whoever can help me make this work?
I installed the Bosch bova 20 ( think it may be same as M20 ) The 20 required the bosch air handler where the 18 can use the current air handler, both do not need a communicating thermostat, and it is recommended not using a nest thermostat.
When it goes into defrost the resistance heaters may overload the inverte, my heaters are 10kw + the running wattage of the unit. I have read of an installer leaving the heaters out (not recommended ), however I plan to add additional breaker to manually drop the heaters during a power outage. This will cause a drop in room temp when defrosting but at least will have heat during the power outage.

On the Bova 20 air handler when the heaters are powered off with the included breaker the control circuit shuts down, the reason I plan additional breaker to isolate the heater coil.

I did a lot of research prior to install. We already had ductwork and did not like the wall hung units. The effiecenticy of the mini splits drops drastically when combined airhandler and ductwork.

I have been completely satisfied with the decision, 2 years and have had a couple power outages during the summer, one during the winter and the Schnieder xw6848+ inverter handled it with ease, (no water heater and any high wattage appliances ) these can be run at opportunity times if necessary.

Hope this helps
Wayne
 
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I know this comment isn't directly on topic, but another option is to heat with gas or wood. Depending on where you live, wood can be free, and it's relatively inexpensive to heat with propane or natural gas (especially considering they cost of inverter and batteries it would need).

I'm able to have a relatively small system, because my heat comes from wood. Even a small wood stove with a small fire creates quite a bit of heat.

Of course, that doesn't address cooling in the summer.

Just my 2¢.
 
I know this comment isn't directly on topic, but another option is to heat with gas or wood. Depending on where you live, wood can be free, and it's relatively inexpensive to heat with propane or natural gas (especially considering they cost of inverter and batteries it would need).

I'm able to have a relatively small system, because my heat comes from wood. Even a small wood stove with a small fire creates quite a bit of heat.

Of course, that doesn't address cooling in the summer.

Just my 2¢.
I agree completely, air conditioning is in most cases for comfort, but really nice to have it. I also keep a supply of wood on hand never know when a failure may occur
 
I agree completely, air conditioning is in most cases for comfort, but really nice to have it. I also keep a supply of wood on hand never know when a failure may occur
My system is not able to run my HVAC, so I have a cheap window unit that I keep around for when the power goes out in the summer. During the day I put it in the living room, and at night it goes into the bedroom. It doesn't keep the whole house cool, but it keeps it livable. It's not really a permanent solution, but it does work.
 
Bigger heat strips usually have their own separate breaker mounted right with them, turn it off.
However, I think some heat pumps will turn them on to defrost themselves, others use a pan and/or compressor heater to do this instead.
I disconnected my heat strips, completely useless in Florida.
 
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