Heat battery for just underfloor heating?

[JohnMo]

1 hour ago, Tilbert said:

65-75mm and it looks like you are proposing 150mm plus floor finish which not something we would be able to recommend

Your not asking them to recommend, a thick concrete, imagine a big storage heater, you can almost dump heat into at any time.  It is a slow heat store. If your house is well insulated the floor temp will rarely be 1 or 2 degrees hotter than the room target temp, so becomes self regulating. If room temp exceeds floor surface temp the floor stops giving heat out.

 

Down side of thick floor, you almost operate at 12 hour delay, but if know that you can play with it. You can batch charge the floor at cheap rates or use excess solar to store away heat etc.

 

Thick floors take a bit of getting used to but don't see any real issues.

[SteamyTea]

It takes around 2.2 MJ to raise a m³ of concrete.

So if 0.1m thick, 0.22 MJ.

A 1 kW heater, delivers 3.6 MJ an hour.

So an hours runner and it has gone up 16⁰C.

Assuming half of that goes into the room i.e 500 W, the column of air above it needs 3.1 kJ to raise up 1⁰C (2.5 m ceiling).

The air will heat up by 1.7⁰C, but the slab will only be raised 8⁰C.

This will obviously change depending on starting conditions, but assuming that the slab starts at 10⁰ C below room temperature, after an hour a greater proportion of energy is heating the air.

Personally I think if a room can significantly change temperature i.e. 4⁰C in 3 hours, there really is not a problem.

 

 

[JohnMo]

41 minutes ago, SteamyTea said:

It takes around 2.2 MJ to raise a m³ of concrete.

So if 0.1m thick, 0.22 MJ.

A 1 kW heater, delivers 3.6 MJ an hour.

So an hours runner and it has gone up 16⁰C.

Assuming half of that goes into the room i.e 500 W, the column of air above it needs 3.1 kJ to raise up 1⁰C (2.5 m ceiling).

The air will heat up by 1.7⁰C, but the slab will only be raised 8⁰C.

This will obviously change depending on starting conditions, but assuming that the slab starts at 10⁰ C below room temperature, after an hour a greater proportion of energy is heating the air.

Personally I think if a room can significantly change temperature i.e. 4⁰C in 3 hours, there really is not a problem.

 

 

Slight problem, the above assumes you 1kW of heat available for each m2 of concrete. My floor works on 0.03kW per m2, i.e. 192m2 and max of 6kW from ASHP.

 

So heat up times are a slower, but once up to temp the heat is just dripped in.

[SteamyTea]

17 minutes ago, JohnMo said:

Slight problem, the above assumes you 1kW of heat available for each m2 of concrete

Oh yes.

But it makes it easy to convert.

 

I am not sure how good 30W/m² is.

It sounds low.

My heating season is around 100 days, and I use an extra 1,500 kWh. So 30 kWh/m².

Divide by 2400 hours, 12.5 W/m².

Under half yours. But it is much warmer where I am. Probably no lower that 8⁰C most of the time. Had 2 frosts last year.

Last year my total energy usage worked out at 7.3 W/m².

I am sure solar could provide all of that.

 

Edited October 2, 2023 by SteamyTea

[JohnMo]

53 minutes ago, SteamyTea said:

I am not sure how good 30W/m² is.

That's what I have available, my peak at -9 was around 16W/m2, but average over the heating season closer to 8W/m2 for the last heating season.

[SteamyTea]

3 minutes ago, JohnMo said:

That's what I have available, my peak at -9 was around 16W/m2, but average over the heating season closer to 8W/m2 for the last heating season.

Interesting, my house, a small terrace, is 1987 vintage, with only minor improvements.

[Tilbert]

On 02/10/2023 at 16:31, JohnMo said:

Your not asking them to recommend, a thick concrete, imagine a big storage heater, you can almost dump heat into at any time.  It is a slow heat store. If your house is well insulated the floor temp will rarely be 1 or 2 degrees hotter than the room target temp, so becomes self regulating. If room temp exceeds floor surface temp the floor stops giving heat out.

 

Down side of thick floor, you almost operate at 12 hour delay, but if know that you can play with it. You can batch charge the floor at cheap rates or use excess solar to store away heat etc.

 

Thick floors take a bit of getting used to but don't see any real issues.

Thanks JohnMo, we’re revisiting with the SE and seems to think we can do a thinner slab. Much appreciated your reply.

[Tilbert]

Thanks all, we’re away at the moment and have been struggling for Internet connection, sometimes.

 

we are re-visiting the slab thickness with the SE.

 

Is there a good web calculator to work out heat loss, size of ASHP needed and ongoing electricity running costs.

 

thanks once again

[saveasteading]

9 minutes ago, Tilbert said:

re-visiting the slab thickness with the SE

Want to discuss the structural side of it?

[SteamyTea]

3 hours ago, Tilbert said:

Is there a good web calculator to work out heat loss, size of ASHP needed and ongoing electricity running costs

Basically no.

There is a heat loss spreadsheet on this site that will get you most of the way there.

[JohnMo]

3 hours ago, Tilbert said:

 

Is there a good web calculator to work out ASHP ongoing electricity running costs

To many variables really. Buffer no buffer, radiators or UFH, insulation levels, running regime, many zones or one zone, outside air temperature, solar PV and if so how much, what angle it's at, also DHW usage patterns and cylinder size, all have a big impact on running cost.

[Tilbert]

Thanks all, I wondered if that was the case. I’ll look ant again when I’m back next week.

 

thanks once again

[John Carroll]

On 07/05/2023 at 22:24, JohnMo said:

Running UFH from an ASHP shouldn't be expensive in fact it's possibly one of the cheapest forms of heating when coupled to UFH. Low flow temperature leads to very good CoP.

 

Attached is section out of our technical manual which gives, flow temperature, heating power and CoP, for reference.

 

By the way you should be adding way more insulation, I doubt you even meet building regs minimum requirement, with 100mm.

 

For UFH you ideally need around 150mm or more.

 

Could you please post the above with Tout extending to its max, say ~ 60/65C.

Thanks.

John

[JohnMo]

1 hour ago, John Carroll said:

 

Could you please post the above with Tout extending to its max, say ~ 60/65C.

Thanks.

John