Off grid radiant heat

rodwilsonsr

Hi,
This is my first post, I'm hoping to find some guidance and some education on my new radiant system. I will list off some things that I believe are important to know before I get into my questions...

1. This is an off grid home, 16 solar panels, 16 batteries
2. The location is northern Vermont which means cold winters
3. The home was built by the previous owner, but was just 4 finished exterior walls and a wood stove for heating. no bathrooms, kitchen or other interior walls.
4. It is well insulated as I have pulled down some pine to expose the exterior walls and verified the insulation
5. The plumber I hired to rough in my plumbing and install the heating system suggested a Rinnai boiler, outdoor reset, Grundfos auto adapt circulators, radiant floor heating with heat transfer plates, foam board insulation between joists and a 1000 gallon propane tank.
6. There are 3 zones, upstairs tstat, downstairs tstat and domestic hot water tank.
7. The house is a full first floor with a 3/4 loft and a cathedral ceiling, it's alot of open space.
8. I did do plumbing/heating 30 years ago, so I am very familiar with hot water baseboard functionality, so I may have some difficulty understanding radiant heat functionality.
9. currently, I am at this home mostly on weekends and plan to move here once the build out for bathrooms and kitchen are done.

Thats the list...here is my apparent issue(s). The installer is MIA, so I'm trying to figure some stuff out myself.
It appears to me that the water is not getting hot enough, quick enough to satisfy the thermostat. for instance, I set the thermostat to 53 when I am going for over a week. When I arrived, I set the thermostat to 64.
The circulator for the first floor ran from 7pm till 8am and was up to 62 degrees. The upstairs was set at 64 and was satisfied at some point during the night.

the outdoor reset was reporting 34 degrees at 8am. The circulator was running for the first floor and the water temp on the boiler was around 115. Every 15'ish minutes the boiler would kick on, heat the water to 145, shut off and within 2-3 minutes the water temp is back down to 120's. And it appeared to just keep repeating this cycle with the room not getting over 62 degrees.

One of my critical variables here is being off grid. I dont have an unlimited supply of electricity. I can add more batteries and panels eventually...but for now, my best thinking is to get the water hotter to heat the space.

I have gotten into the service menu of the Rinnai, but there are many settings that I am not clear about and what impact they will have. I have tried to up the max temp, up the min temp, but I think the outdoor reset keeps screwing with me.

I have talked to my installer before he went MIA, and once he really considered that I dont have unlimited electricity, he was going to unhook the outdoor reset and just work the boiler off high/low limits when the tstat calls for heat, I guess similar to what I remember with hot water baseboard systems back in the day. I have tried to eliminate the outdoor reset, but I dont know the system well enough to be confident I did it correctly.

Does anyone have any suggestions on the optimal settings, being off grid, limited electricity and having a functional heating system?
Maybe there is a way to live in harmony with an outdoor reset, off grid and have it not suck so much electricity.
It's going to be close to 0 degrees next week and I am in a bit of panic mode now.

Thank you all for reading this...looking forward to the responses.
RW.

Zman

Your recovery times for bringing the space up to temp sound about right for an outdoor reset system.I understand why you are doing deep setbacks, is there a way to remotely change the temp so it is warm when you arrive? You could also install an outdoor reset override switch for when you arrive and want faster recovery.

Do you know how much energy your system is using? It would be helpful to know how much you use for circulation and boiler(got an amp meter). Depending on these numbers, you may decide that outdoor reset and long cycles use too much power. Do you have issues with running out of power?

Jamie Hall

It does seem as though the system is working reasonably well. The boiler cycling on and off is actually good news, believe it or not, as it indicates that there is enough boiler capacity to handle the load when it gets colder. Further, you at least have relatively low current draw equipment, which is a plus.

Outdoor reset will automatically increase the boiler's temperature setpoint when it's colder outside. Somewhere in the manuals for that boiler there will be instructions for how to adjust the curve -- the way it responds to outdoor temperature, and you may want to increase the temperatures the curve is set for if it isn't maintaining the space temperatures you want.

@Zman has the key question for you: how much energy does this system actually use when it's running? And, obviously related to that, do you have enough battery capacity to keep it running 24/7 when it is somewhere below 10 all day and cloudy and windy for three days in a row? And do you have enough solar panel capacity to recharge those batteries in a few hours when the sun actually does reappear?

EBEBRATT-Ed

Problem is the boiler and pumps use basically the same energy running at low or high input. Low input and balancing the heat loss go hand in hand with radiant heat but not with limited power usage.

And extended set backs don't work well with radiant either.

It will be easier to deal with when you are living their but for know it is an issue.

If the controls will not allow the radiant to overheat on high water temp I would try getting rid of the outdoor reset and try that.

A monitoring system to control the heat from your phone so you can watch the temps and and the boiler is a good idea

jumper

How long do you intend to live there? Off grid photovoltaic heat requires storage.
Two approaches.
One is to store a lot of very hot water with a lot of panels. You want at least ten days of storage.
The other way is to store heat in ground below your shack. That way you can store summer hours.
In the olden days when off peak electricity was inexpensive some industrial facilities did that.

hot_rod

Sounds like you could us a large thermal solar array. Higher efficiency and easier to store thermal energy if you have enough tank space, or high mass slab. There are a number of thermal solar homes in northern Wisconsin that make it through the winter with solar thermal only.

Years ago the off grid radiant homes I worked on used Paloma tankless heaters as they did not require any power, they were not condensing, high efficiency however, propane standing pilot. Then the only electricity required was for a high head pump. The new ECM style would maybe be around 50- 60W. Line voltage stat to eliminate transformer draw.

pecmsg

using an ECM Pump motor will lower the electrical usage quite a bit. 

Jamie Hall

Well, yes. Solar thermal would be the way to go. I have a tendency to answer the OP's questions, and not propose alternatives -- but solar thermal would be the way. No question.

In fact, my father-in -law, since passed away, and I did several 100% solar thermal, near 100% passive (only a single fan) houses in northern Vermont. So far as I know, they are still working just fine.

It might not even be too late to do it, if the house is still partly finished...

hot_rod

Sounds like you have ECM circulators so that keeps pumping power to a minimum.

Keeping the boiler running and modulating the blower speed would be the best way to conserve electricity. Every time they stop and start they pull more current as the combustion fan inside does a pre, post purge at it's highest speed, highest current draw.

See if that boiler has a "boost" function. Here is how it works on the Lochinvar Knight boilers.
It may be called something else on other brands. Keep adjusting all parameters until you get the longest run cycles possible.

Slow and steady will be the best way to run. If you raise temperature of the boiler, it may cover the load faster, but could also increase cycling. So if you have a programable boost start conservatively with the steps.