Use UFH to store heat?

Wobblydeb

Now that I'm thinking about how to get best use out of solar panels, the obvious win to me is a flooring system akin to a storage heater.

One that uses the electricity produced during the day to "charge" the floor ready to emit heat in the evening.

Does such a thing exist?

I know there is solar thermal, but we're putting in solar PV as there are more things in our house use electricity than hot water....

zeupater

Wobblydeb wrote: »

Now that I'm thinking about how to get best use out of solar panels, the obvious win to me is a flooring system akin to a storage heater.

One that uses the electricity produced during the day to "charge" the floor ready to emit heat in the evening.

Does such a thing exist?

I know there is solar thermal, but we're putting in solar PV as there are more things in our house use electricity than hot water....

Hi

Yes, it will (/can) work, but at the time of year you want heating it'll make little/no difference ...

Have you thought about diverting excess generation to heat hot water with an immersion heater (if you have GCH & a cylinder) ... a couple of years to go before they make financial sense, but home batteries are on their way which also soak-up excess generation ... there's also the possibility of helping with EV charging if you're typically at home when the sun's shining ....

If it's definitely heat that you're looking for, a few of the members on the forum have installed small heat-pumps specifically to work in tandem with solar PV ... see this forum thread ... so there are a number of options available which would probably make better use of energy than the UF heating (presumably bathroom?) and should normally be given a higher priority, but a lot depends on what you have, what you want to do & what's considered affordable!

HTH
Z

Wobblydeb

Thanks zeupater. I guess I'm thinking I will get more power out of the system than perhaps the reality on a miserable November day

We've planned for an Eddi unit (same thing as Immersun) as we have a hot water cylinder with an immersion switch.

I'm starting to wonder if I was hasty with that though, as the cylinder is primarily gas powered. If I am understanding this correctly, then I pay far less for gas per kWh than elec, so it is quite economical to heat the cylinder from our condensing boiler, and the Eddi will have a very long payback period?

Wobblydeb

But of course my cylinder runs both my hot water and my radiators, doesn't it?? :doh:

So, if I heat the water, I can heat the house. I'm just not certain I can do it without pulling in additional electricity and gas to run the system.

At the moment the heating is set to come on at 4pm and the hot water at 6.30pm. I want the solar pv to run most of the day and stop the gas from being needed at 4pm.....

I also don't want the immersion to run from the grid AT ALL. If I need more power I want it to come from the gas....

zeupater

Wobblydeb wrote: »

But of course my cylinder runs both my hot water and my radiators, doesn't it?? :doh:

So, if I heat the water, I can heat the house. I'm just not certain I can do it without pulling in additional electricity and gas to run the system.

At the moment the heating is set to come on at 4pm and the hot water at 6.30pm. I want the solar pv to run most of the day and stop the gas from being needed at 4pm.....

I also don't want the immersion to run from the grid AT ALL. If I need more power I want it to come from the gas....

Hi

You will (/should) have the ability to heat hot water without running the radiators ... isn't this what you do in the summer? ...

Much will depend on the capacity & orientation of your solar system, but effectively you should be able to provide most of your DHW from solar for approx 6 months of the year (therefore need little/no gas) & have it help-out to varying degrees for the other half, so using less gas ...

I'm not familiar with the Eddi system, but as long as it's a proportional diversion system (like the immersun) you shouldn't need to worry about the immersion coil using electricity when the panels aren't generating, although the immersion's capacity to heat the cylinder may be limited by position and/or length ...

On the timing & PV capacity ... a GCH boiler will normally provide somewhere in the range of 15-30kW of heat to the system when first heating, reducing to (say) 5-8kW when the radiators have warmed up .... a 4kWp PV array in the winter may provide as much energy over the entire day as the boiler will in a few minutes, so forget about heating the house with the PV & an immersion. What many with this set-up do is use diverted PV energy to heat water to a temperature which is above the setting of the GCH thermostat on the cylinder and set the DHW timer to work for about 1 hour somewhere after sunset ... this way, if the water is hot, there's no call for gas and if not, the GCH just tops-up the water temperature .... of course, in winter the top-up will be significant & in summer it'll probably be a rare occurrence!

HTH
Z

Wobblydeb

zeupater wrote: »

You will (/should) have the ability to heat hot water without running the radiators ... isn't this what you do in the summer? ...

Yup - I was just slapping my head at being so stupid for seeking another method of heating my house when I've got a cylinder which can do it. I'm only just getting accustomed to this system after having a combi boiler for years

zeupater wrote: »

I'm not familiar with the Eddi system, but as long as it's a proportional diversion system (like the immersun) you shouldn't need to worry about the immersion coil using electricity when the panels aren't generating, although the immersion's capacity to heat the cylinder may be limited by position and/or length ...

The Eddi was created by the same guys as the Immersun, and looks like a copy of it. So I guess it is a proportional diversion system. The bit I don't understand is how I switch on the immersion without it ever drawing from the mains? Yes, I need to go read the Eddi manual....

ASavvyBuyer

Wobblydeb wrote: »

The Eddi was created by the same guys as the Immersun, and looks like a copy of it. So I guess it is a proportional diversion system. The bit I don't understand is how I switch on the immersion without it ever drawing from the mains? Yes, I need to go read the Eddi manual....

Wow, that Eddi diverter is expensive compared to some of the other diverters. £365 inc VAT plus fitting costs.

Be interesting to see what the actual payback period is when you compare it with the lower cost of gas.

Glad our diverter only cost £30, even though it is not proportional, we still get all the hot water we need for "free" from April till Spetember.

Wobblydeb

ASavvyBuyer wrote: »

Wow, that Eddi diverter is expensive compared to some of the other diverters. £365 inc VAT plus fitting costs.

Yup, I thought it was rather expensive. However, we are getting the Zappi (EV charger) which is from the same company. As a result, they can be linked and prioirty can be set from either device - controlling how they split the surplus energy.

I didn't explore whether that could be achieved using a different / cheaper diverter ...... which perhaps I should have done!

Wobblydeb

Hmmmmmm I am now starting to think that heating up my cylinder will NOT provide me with hot radiators. I think there is a pump underneath the cylinder that (along with a diverter valve) sends hot water direct from the boiler to the radiators without getting the cylinder involved.... :huh:

zeupater

Wobblydeb wrote: »

Hmmmmmm I am now starting to think that heating up my cylinder will NOT provide me with hot radiators. I think there is a pump underneath the cylinder that (along with a diverter valve) sends hot water direct from the boiler to the radiators without getting the cylinder involved.... :huh:

Hi

Yes, it should either have 1 x 3-port motorised valve, or 2 x 2-port ones, depending on the circuit ... a 3 port setup allows heating of house or water, not both at the same time & the 2 port setup allows either or both, but neither are designed to have the DHW cylinder provide heat to the radiators ... a heat-bank (as used with heatpumps etc) does do this, but they're normally much larger than a standard cylinder, so you'd certainly know if you had one!

HTH
Z

pinnks

I am an immerSUN man and like the product. It does look as though eddi is pretty much a clone, so while expensive compared to some of the competition, it should be a good product.

My PV system is quite large spilt over two rooves signature below), but I get all my hot water for 6 months and used to get a good percentage over the other 6 months - I have batted on about it on here a few times if you search my posts.

Last year I put 1.8kW of UFH in my kitchen and wired it into the immerSUN. It only went live towards the end of the year and I didn't get much diverted to it at all as anything available went to the hot water.

This year I decided to change the priority in the immerSUN to push any surplus to the UFH in priority to the immersion on the basis that the water will be heated by gas anyway in winter, so I could make better use of the surplus by warming the floor. This is working well and on reasonable days the floor gets up to 22+ degrees and is kept there all day even in February. On days like today (generated 17kWh) we had a warm floor all day, got hot water and did the washing and drying and still exported 1kWh over the day.

Also, bear in mind that if you use the gas boiler to heat water when the radiators are off you have high losses in the pipes to and from the tank. My experience based on my gas consumption records going back to 2009 is that I save about £70 to £80 on gas over the summer months using the immerSUN and another £20 or so over the rest of the year, so my £350 investment 5 years ago is pretty much paid for now.

So, don't despair and play around with how best to use your surplus and change the priorities at different times of the year to max out best use of PV. It will repay itself and above all you will be happy that you are getting hot whatever for free.

But the main thing is that you have spent that money now, so just use the kit and don't dwell on it...

:beer::beer: