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Topic Title: Underfloor heating
Topic Summary: Diversity?
Created On: 21 March 2013 06:30 PM
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 21 March 2013 06:30 PM
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Avatar for stateit.
stateit

Posts: 2185
Joined: 15 April 2005

Hi Guys,

Muggins here has a customer wanting electric UFH throughout their 140m2 extension.

They're off grid for gas, don't want the 'expense' of another oil boiler, don't want the 'expense' of 3-phase from a couple of fields away.

I'm trying to discourage them from electric UFH as their existing house / outbuildings with its UFH are choking their 100A supply up to the limit as it is.

So, having done my floor area calcs to their preferred 200 W/m2 cable, I've come up with a figure of 95A for 110m2 of cabling.

I can't find any mention of Diversity for UFH.

Any thoughts on the matter?

-------------------------
S George
http://www.sg-electrical.com
 21 March 2013 07:22 PM
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broadgage

Posts: 1293
Joined: 07 August 2007

I dont think that any diversity is allowable.
What stops the entire load being run at the same time ? nothing I suspect.

200 watts per square metre sounds a lot, and it would probably not run continualy very often.
But in very cold weather, or following a power cut, or after the owners return fom a winter holiday, it could draw full load for hours.

Might not be used much after they get the bill ! several £ an hour
 21 March 2013 08:29 PM
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Zs

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Diversity is not cast in stone. Common sense is worth a great deal in such a case as this.

This is where you need to ask about the usage of the system and then, probably, diversify the hell out of it.

But, aside from the massive diversity you may well be able to include are they planning on using electric underfloor heating as the primary source of heat? Really, it isn't going to work efficiently.

I have a meter on my home electrics and electric underfloor in the kitchen. Warmboards below the mat. It costs at least 6p an hour to have the kitchen underfloor on and I guess we are talking less than three square metres. It takes the chill off, but does not create a warm ambience.

Zs
 21 March 2013 08:35 PM
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OMS

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At 200w/m2,it'll be like Barbados all year round - and it would probably be cheaper to move there than pay the bill on that lot as direct acting on peak heating.

As Zs suggested, be very careful about applying diversity to that lot, if you don't know just how the client intends using it. As a starting point I would work on the basis you have very little diversity ubless you can calculate otherwise.

Out of interest,how is the extension going through Part L with electric UF heating ?

regards

OMS

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Failure is always an option
 21 March 2013 09:24 PM
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stateit

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Originally posted by: OMS


Out of interest,how is the extension going through Part L with electric UF heating ?


How any of the build has got this far through BC inspections makes me wonder.... I'll ask the customer about his experience of the Planning Process tomorrow OMS, thanks for that thought.

Zs: Primary heating source: Yes.

OMS: 200W/m2: I know...

I imagine at planning stage it was assumed 'usual' forms of CH would be used.

They're the type of customer that get an idea and just steam ahead with it.

Anyway, electricity supply regardless, my knees and back are saying this month that he's not getting 100+m2 of UFH.

When he sees my load calcs for the UFH, and when I suggest how much it will cost to have installed, I think a new oil boiler may seem cheaper than originally thought ...

-------------------------
S George
http://www.sg-electrical.com

Edited: 21 March 2013 at 09:34 PM by stateit
 21 March 2013 10:20 PM
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peteTLM

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I done a house in chigwell a couple of years back. Massive extension the size of the house again. Ended up with 6 bedrooms, and 4 bathrooms all had underfloor electric heating added against my best advice.
Long story short- electric bill was now MASSIVE.
same story, didnt want to change boiler, blah blah blah.
The wished they could have gone back in time after 9 months worth of bills, would have paid for the heating alterations to be done properly.

200w/m is for primary heating- same as the house above.

-------------------------
----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 21 March 2013 10:38 PM
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stateit

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Yep, barking...

They want an ASHP to help with the new swimming pool though...But not anywhere else

-------------------------
S George
http://www.sg-electrical.com
 21 March 2013 10:55 PM
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peteTLM

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by all means steer them towards underfloor heating, just of the wet central heating type instead...............................

-------------------------
----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 22 March 2013 08:35 AM
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bartonp

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Given the likely bills, how about GSHP via the'green deal' instead?
I'll get my coat.....
 22 March 2013 09:39 AM
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impvan

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If they're open to the idea of a heatpump, then why not feed wet UFH from that? Low-grade heat, perfect for the job..

Alternatively, without upgrading the oil boiler, get a large ~500L buffer cylinder "thermal store" and heat this up during the night when the boiler demand is low. This can then bleed heat through to the floor during the day.
 22 March 2013 10:12 AM
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AJJewsbury

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Alternatively, without upgrading the oil boiler, get a large ~500L buffer cylinder "thermal store" and heat this up during the night when the boiler demand is low. This can then bleed heat through to the floor during the day.

Nice idea, but I don't think that'll stack up with such a large load.

140m² at 200W/m² comes to 28kW - if you want it on for say 10 hours/day that's 280kWh you'd need to store.

Say (being optimistic) you could get the thermal store up to 90 degrees and the UFH would work down to say 30 degrees - so you can pull 60 degree difference from it - at 4.18 J/gK or 1.16 kWh/m³K I reckon 500 litres could store about 34.5kWh - or about 12% of what you'd need. Or of you like, the 500 litre store would run the UFH for less than an hour and a quarter.

- Andy.
 22 March 2013 10:32 AM
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Parsley

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Originally posted by: bartonp



Given the likely bills, how about GSHP via the'green deal' instead?

I'll get my coat.....


Would the cost of a GSHP meet the green deals golden rule criteria?

Regards
 22 March 2013 10:35 AM
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broadgage

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Originally posted by: AJJewsbury

Alternatively, without upgrading the oil boiler, get a large ~500L buffer cylinder "thermal store" and heat this up during the night when the boiler demand is low. This can then bleed heat through to the floor during the day.


Nice idea, but I don't think that'll stack up with such a large load.



140m² at 200W/m² comes to 28kW - if you want it on for say 10 hours/day that's 280kWh you'd need to store.



Say (being optimistic) you could get the thermal store up to 90 degrees and the UFH would work down to say 30 degrees - so you can pull 60 degree difference from it - at 4.18 J/gK or 1.16 kWh/m³K I reckon 500 litres could store about 34.5kWh - or about 12% of what you'd need. Or of you like, the 500 litre store would run the UFH for less than an hour and a quarter.



- Andy.


I feel that your calculations are unduly pessimistic.
It would seem that you assume that the entire heating load is to be supplied from the thermal store.
In fact, surely most of the demand would come from the boiler, with the thermal store only being called on when the demand exceeds the boiler capacity.
With a 25KW boiler (a very common capacity for domestic units) only a few KW would be needed from the thermal store, or when the boiler was heating bathwater. The store being filled when the boiler demand was less.
The boiler would run for relatively long times at full load and probably be more efficient and less liable to breakdown than with continual on/off cycling.
Another option would be to meet the demand almost entirely from the oil boiler, and supplement this with an electric boiler when needed.
This would meet virtually all the demand from oil, which is cheaper than electricity, and ensure ample heating even on the probably rare times when heating demand exceeds the boiler capacity.
 22 March 2013 10:58 AM
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AJJewsbury

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I feel that your calculations are unduly pessimistic.

Maybe - I was just working to what I thought was the suggested arrangement.

In ball park figures (on a cold day), the new UFH might want say 280kWh/day and a 25kW boiler running flat out continuously could produce an absolute maximum of 600kWh - leaving 320kWh for the original building - perhaps 20kW for 16 hrs/day - so could be plausible if the original building requires little more heating than the new extension.

It's all madness anyway. We've got the technology to build to a standard that should require no more than 15kWh/m²/year to heat - this system sounds like it'll use that much energy in a week.

- Andy.
 22 March 2013 12:59 PM
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Zs

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Originally posted by: bartonp



Given the likely bills, how about GSHP via the'green deal' instead?

I'll get my coat.....


NO! Want to see some electricity bills for such homes? They are shocking. At the moment I do not think the UK is equipped to design GSHP or ASHP systems which reduce energy costs and warm a home to a comfortable level. We all know it is possible but is isn't happening here. I have yet to meet a system - water underfloor or radiators which is performing in accordance with the manufacturers' blurbs.

Zs
 22 March 2013 01:45 PM
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bartonp

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Originally posted by: Zs

Originally posted by: bartonp



[IMG][/IMG]



Given the likely bills, how about GSHP via the'green deal' instead?



I'll get my coat.....




NO! Want to see some electricity bills for such homes? They are shocking. At the moment I do not think the UK is equipped to design GSHP or ASHP systems which reduce energy costs and warm a home to a comfortable level. We all know it is possible but is isn't happening here. I have yet to meet a system - water underfloor or radiators which is performing in accordance with the manufacturers' blurbs.



Zs


Yet so see one where the primary cct hasn't leaked or isn't leaking...
 22 March 2013 03:44 PM
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rocknroll

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There is nothing wrong with heat pumps and to say they dont work well in the UK is twaddle, there are many success stories of systems in operation here that work well, for decades now heat pumps have been used in areas much colder than here, Scandinavia, Canada, other northern european countries etc; with great success.

One of the main problems is bad design and installation short cuts, undersized units, owners not having a clue how to set up controls to take advantage of them, and to contact clueless contractors like electricians because it is cheaper than an experienced heat pump person is always going to be a failure in my book.

There a serious lifestyle issue as well, in countries where they have been using heat pumps for eons if it gets a bit cool they throw on a jumper but here its turn up the heating to max, I think someone commented that the UK loves their 30 degree living where everywhere else they contend with 20 degree living.

One my friends has a little known unit from China and that is SinoCredo and it works really well.

Some useful information here;
http://www.heatpumps.co.uk/index.html


regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 22 March 2013 at 04:15 PM by rocknroll
 22 March 2013 06:11 PM
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stateit

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Well, after discussion today:

UFH will be secondary heat source in 3 rooms, Off-peak storage in two, wet underfloor in the other room run off existing boiler.

In the 3 rooms with UFH as secondary there will be air-con (he knows an air-con man...)

He doesn't rate ASHP for primary in the winter when it's neede,(he discussed a 25kW setup) but rates it as OK to help the pool heating in the summer.

Fair-dos I s'pose. It's his money.

-------------------------
S George
http://www.sg-electrical.com
 25 March 2013 11:25 AM
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Avatar for OMS.
OMS

Posts: 19661
Joined: 23 March 2004

Originally posted by: Zs

Originally posted by: bartonp

[IMG][/IMG]

Given the likely bills, how about GSHP via the'green deal' instead?

I'll get my coat.....


NO! Want to see some electricity bills for such homes? They are shocking. At the moment I do not think the UK is equipped to design GSHP or ASHP systems which reduce energy costs and warm a home to a comfortable level. We all know it is possible but is isn't happening here. I have yet to meet a system - water underfloor or radiators which is performing in accordance with the manufacturers' blurbs.

Zs


The electricity bills are shocking because the systems are designed installed and operated by idiots.

The UK has an ideal climate for ASHP or GSHP and meeting comfort levels is an absolute doddle - if you know what you are doing

There are plenty of UK horror stories about heat pump systems but see my opening sentence.

The key is to examine the manufacturers blurbs and drill down and challenge them on the low temperature performance (if it's direct acting) or the part load performance if you are going to deploy "buffering".

For those systems that don't work, it most usually a total mismatch between the heat pump performance and the building demands - with the demands being grossly underestimated by the designer and the heat pump performance being "cleverly" stated by the manufacturer at optimum conditions.

It's mature technology, being widely used across Europe, in often far more extreme conditions than the UK climate - but as I keep saying it needs to be designed right, selected right, installed right and commissioned right - just like any other system.

What you can't do is slap in a heating system based on gas fired or oil fired heat generation and then assume a heat pump can be a direct replacement for those heat generators (not unless you want horrific electricity bills - which is where we came in I guess.)

I'll send you some details of a school that has ASHP systems - annually they consume less kWh than the school generates from roof mounted PV - in essence zero carbon - and internal comfort levels have remained within spec (both summer and winter) since handover about 2 years back (allowing for seasonal commissioning during the 12 months defects period).

I suspect your experience is to run into the "problem" jobs - not those that work perfectly well.

Regards

OMS

-------------------------
Failure is always an option
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