Solar heating project equipment and calculations

[df0rster]

Which is why its so ridiculously cheap to heat water using eco mode. Funny you should compare it to a fridge; since I installed my electricity monitor 24 days ago my fridge has used 45.62kWh and the water heater has used 27.88kWh. I expect the water heater to use a lot less electricity has the weather warms up outside.

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Interesting.

I guess the bottom line is I should get 4200 btuh from the heat pump only. Which isn’t nearly enough to heat my house. But I’ll use less than 12 kWh per day running it 24 hours if it only uses 400 watts. That should be enough to keep the floors semi warm. I could even use another 20 kWh from the heating elements and be within my 30 kWh goal.

Rethinking this a little, it seems like for my application the hpwh is gong to give me about 800 watts “free” because of the power factor. (1200w-400w). Going back to another point a poster made, I can buy 800 watts worth of panels for a lot less than $1200 and just use a conventional water heater.

I’m still not sure I’m thinking about it correctly.

[Ampster]

I guess the bottom line is I should get 4200 btuh from the heat pump only. Which isn’t nearly enough to heat my house. But I’ll use less than 12 kWh per day running it 24 hours if it only uses 400 watts. That should be enough to keep the floors semi warm. I could even use another 20 kWh from the heating elements and be within my 30 kWh goal.

Rethinking this a little, it seems like for my application the hpwh is gong to give me about 800 watts “free” because of the power factor. (1200w-400w). Going back to another point a poster made, I can buy 800 watts worth of panels for a lot less than $1200 and just use a conventional water heater.

I’m still not sure I’m thinking about it correctly.

I am definitely one of the fanatical guys that PNPmacnab was referring to in regards to my feelings about HPWHs. However I do not believe they are the greatest thing in the world but I have looked at the numbers. The numbers, especially the kWhs and the BTUs/h are why they can make sense in many situations where you want to use electricity to make something warm.
The HPWH could be saving you that 800 Watts every hour that you are using it, but the 800 Watts of solar panels at the most will get you five hours of production which is 4kWh. The heating element could use that 4kWh up in just an hour. Looking at it another way, you would get four times the BTUs in your home for every kWh conumed by using a HPWH versus a using a heating element.

[df0rster]

I am definitely one of the fanatical guys that PNPmacnab was referring to in regards to my feelings about HPWHs. However I do not believe they are the greatest thing in the world but I have looked at the numbers. The numbers, especially the kWhs and the BTUs/h are why they can make sense in many situations where you want to use electricity to make something warm.
The HPWH could be saving you that 800 Watts every hour that you are using it, but the 800 Watts of solar panels at the most will get you five hours of production which is 4kWh. The heating element could use that 4kWh up in just an hour. Looking at it another way, you would get four times the BTUs in your home for every kWh conumed by using a HPWH versus a using a heating element.

Oh I understand and agree with that. I have an 80 gallon AO smith heater installed already when we built. It’s got 9kw of heating elements. I’ve never had it turned on because it’s a buffer tank for my geo hot water generator. I’m thinking of plumbing it in to the floor heat using an open direct concept that I’ve seen online. It allows domestic hot water and radiant heat to use the same water heater. Since it is already installed I’ll at least be able to test the system out and monitor consumption to see exactly how much kwh it takes to keep the floors warm. Then it might be easier to figure out if the hpwh is worth the expense. I think if I can use it for domestic and radiant like I’m planning then it would really be worth the expense. And would help with my goal of eventually being off grid. My current setup uses an electric tankless in series with the buffer tank and that tankless uses up to 27kw so is not off grid friendly at all.

[J.P.M.]

Oh I understand and agree with that. I have an 80 gallon AO smith heater installed already when we built. It’s got 9kw of heating elements. I’ve never had it turned on because it’s a buffer tank for my geo hot water generator. I’m thinking of plumbing it in to the floor heat using an open direct concept that I’ve seen online. It allows domestic hot water and radiant heat to use the same water heater. Since it is already installed I’ll at least be able to test the system out and monitor consumption to see exactly how much kwh it takes to keep the floors warm. Then it might be easier to figure out if the hpwh is worth the expense. I think if I can use it for domestic and radiant like I’m planning then it would really be worth the expense. And would help with my goal of eventually being off grid. My current setup uses an electric tankless in series with the buffer tank and that tankless uses up to 27kw so is not off grid friendly at all.

I'd look carefully with respect to that dual application. Many plumbing codes do not allow using one source for 2 uses when one of them is for potable water use and the other one is not. Maybe if the radiant floor heat went through a HX (and that may require what's called a double wall HX if code would allow it at all). Also, space heating systems that use water are usually closed or at least don't use much make up water. One reason for that is (semi) closed systems (or at least not open systems) stay cleaner (non fouled) a lot longer than open systems.

What you write of is possible, but without a whole lot of ancillary equipment including controls to fail and HX's to foul up in ways that are inevitable but unknown to most folks, you'll be creating a plumber's nightmare and a world of hurt for a hot water radiant floor heating system. On line stuff is unvetted. Just like u-tube, it's the new idiot's bible. What you describe reads like another example of the B.S. that goes on.

[df0rster]

I'd look carefully with respect to that dual application. Many plumbing codes do not allow using one source for 2 uses when one of them is for potable water use and the other one is not. Maybe if the radiant floor heat went through a HX (and that may require what's called a double wall HX if code would allow it at all). Also, space heating systems that use water are usually closed or at least don't use much make up water. One reason for that is (semi) closed systems (or at least not open systems) stay cleaner (non fouled) a lot longer than open systems.

What you write of is possible, but without a whole lot of ancillary equipment including controls to fail and HX's to foul up in ways that are inevitable but unknown to most folks, you'll be creating a plumber's nightmare and a world of hurt for a hot water radiant floor heating system. On line stuff is unvetted. Just like u-tube, it's the new idiot's bible. What you describe reads like another example of the B.S. that goes on.

I have been researching the open direct system. Radiantec.com claim to have developed the system. Or at least they sell components to build it. They claim it is the best way to do radiant floor heating. I will try to post their schematic. It is very simple and claimed to be allowed by code.

to implement it in my existing closed system I just have to add a check valve and a couple it Ts into my floor manifold. I also have an incoming whole house filter and a screen/filter on the floor system. I plan to flush it good before any attempt.