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Author Topic: ASHP setup with rads and UFH  (Read 10005 times)
flip
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« Reply #30 on: January 26, 2011, 01:06:16 PM »

As for the size of house:

Ground floor with UFH = 78m2
First with rads = 104m2
Attic room with rads = 80m2
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Baz
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« Reply #31 on: January 26, 2011, 01:26:58 PM »

One of the other threads on UFH showed calculations based on 30W/m2 being inadequate. Whether it is UFH or radiators isn't the point, the heat input you have is ok for the ground floor, on its own which I think you found. However it would need to be running continuously and at a cop of 2 to handle the upstairs plus attic.
Another viewpoint is you have 8 radiators. 3KW input, cop of 3 to be very generous, and you've only got 1KW per rad and a bit spare for the pipes. You just haven't got enough to bask in tropical conditions. Cut down to 3 radiators and max of 3 rooms and you stand a chance.
Superwarm duvets are peanuts at the moment so no real need to heat bedrooms at all.
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dhaslam
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« Reply #32 on: January 26, 2011, 03:16:07 PM »

Normally I would just  let the buffer tank try to reach  whatever temperature it can reach, i.e set  it to a high setting.   However if it is using 3 kW of  daytime electricity  then that may not be such a good idea unless you restrict the running time  a bit on the timer.     

I would still  urge you to first establish whether it is actually producing the expected output and also if possible to compare  the rate of heat increase  at different temperatures as it warms up.     

My heat pump seems to  work better when the buffer tank is 40C or higher and it can't be set  with a return temperature lower than 40C.     Yours may have different characteristics  and may possibly be far more efficient at  lower temperatures.    You cannot go by manufacturers figures, they are only a rough guide.       
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
flip
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« Reply #33 on: January 27, 2011, 06:30:46 AM »

The pump will warm up the 200 litre buffer tank from around 26 degC to 40 degC in about 25mins. I tried it last night.
When you run the pump off the buffer is the problem, with the rads on the first floor and UFH the temp will not get higher than 37, therefore runs all the time. I have turned doen the stats on the rads where not required to try this also.

My next train of thought is to leave the ground floor UFH on 24/7 and also the first floor rads. Although they are only warm, they do make a big difference to the upstairs temp, but then the ASHP will never go off I think as it cannot get to its set return temp.

Will the temp off the house eventually level out so the pump will be able to reach 40deg return?
Think its worth a try?

Other thought is to fit bigger rads where needed. I could work out BTU required and double it maybe?

The manual talks about changing pump curves to suit rads, UFH etc. For example see attached doc. Any ideas on changing this?

* pump curve data.xls (97.5 KB - downloaded 138 times.)
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flip
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« Reply #34 on: January 27, 2011, 01:02:31 PM »

If I fitted a thermostatic mixing valve and pump to the ufh with a setting of 40, and turned the pump up to 55 degC, would it not give a better return temp to the buffer and in this way I could perhaps have warmer water going to the rads?
How does it work??
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Baz
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« Reply #35 on: January 27, 2011, 01:52:01 PM »

Trying to run the UFH at the same time as the radiatirs will make it worse.
Getting bigger radiators will make it worse.
Turning down the radiators is no good as they won't get hot enough to turn off. You need to turn them off.
Your test on the tank alone shows you have very roughly 7kw coming in from your heat pump so COP is >2 so equivalent to half price electricity so close to cost of gas so not a bad deal.
However you simply don't have enough heat available unless you run the pump longer.
You probably should set the pump temp to max, set the pump timer to run all the time E7 is on, turn off half the radiators. Then see if the tank is still hot in the morning. If it is hot you can open another radiator, or set the ufh timer to run for a short period overnight to store the cheap heat in the floor.
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cornishben
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« Reply #36 on: January 27, 2011, 03:18:53 PM »

Would a solution be to split the UFH/rad circuit and have seperate timed pumps for each?  I know this depends on the accessibility of everything post-install.  This is what I'm thinking about for our ASHP/rads/UFH, the idea being that I could run the UFH overnight on Eco7 to warm up the slab in the main living area and then run the rads separately later in the day. 

This might be a compromise solution and mean you get enough heat for each, although it depends on how you use the space relative to the UFH/rad locations I guess
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dhaslam
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« Reply #37 on: January 27, 2011, 03:42:16 PM »

It is a little surprising that the radiators can take so much heat.   8kW is not an enormous output but at the lowish water temperatures the  radiators shouldn't be capable   of using more than one kW each.    Also a continuous output of 1 kW in a bedroom should make it fairly warm.   It is good to confirm the output of the heat pump because it does  suggest that  house is taking too much  energy to heat it.   Are you sure that the insulation in the house is installed properly and adequate?     
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
flip
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« Reply #38 on: January 27, 2011, 11:29:28 PM »

The house is brand new build,so no issues insulation, both in slab, walls & ceilings.

Today I have turned off un-neccessary rads and left ufh on. Pump is at 40deg return and it does reach this temp, then goes off for 10 mins dropping to 37 and goes again to 40 in around 20mins.

House is nice and warm so good result really.

I would like to increase the rad size in 2 rooms though because one is 1200 x 600 single convection and i think it should be double??

Going to leave on all night to see how it goes.
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dhaslam
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« Reply #39 on: January 28, 2011, 12:06:33 AM »

Changing from single to double panel  will add about 50% to the output  as well as giving more diffused heat, at a guess they will be north facing rooms  that always need twice as much heat  as south facing.  Another common  problem with  radiator circuits is that  they may not  be set up as a balanced return system so distant radiators can be quite a bit cooler than close ones and this can really only be corrected  afterward by fitting larger sizes.   It is specially a nuisance when water temperatures are not very high anyway.

My last house  had  seventeen  radiators running off the sitting room  stove and four of the radiators were added in different places to make up  for  a mixture of mistakes by the plumber and builder, not least of which was leaving the insulation out of two outside  walls. 

   
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
flip
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« Reply #40 on: January 28, 2011, 07:26:31 AM »

Rads are pretty constant heat wise all round, I turn the flows down to compensate and force water to other areas as advised by heat engineer and it works, the hotter ones are turned down 50% and in turn they feed a bit more to otheres. Takes a lot of playing around to get the right balance.
I have calcualted BTU's for the rooms and the rads are sized correct, but I think need to be oversize for ASHP?

Did not leave on all night last night, off at 10pm and back on 5am this morn with 1st floor rads on at 5pm. Also turned pump up to 42 degC to see effect it has.
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mpooley
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« Reply #41 on: February 09, 2011, 05:41:04 PM »

HI
I have just read this thread for the first time and am a total begginer in ASHP as Im just getting quotes for a sytem in my house:
So basically i know nothing!

but just a few points that seem obvious but I cant see anywhere in the thread.

Have you got calcs for heating requirement in the house? its a fairly big house are you sure the ASHP is the correct size?
also you seem to not want to run it for long ? (not sure im correct here )
how many KWH of electric are you using on an average day?

I always assumed this type of system was run almost continuously- what i mean by that is left on say 18-20hrs/day with just the room stats in control.
UHF needs to be left on at least 18hrs a day and normal sized rads are going to need twice the time on to give off the same heat.

I am doing an experiment at the moment where my oil boiler is running at 40c flow to mainly rads- I have a larger house than yours in an exposed position but with good insulation. My calcs say i need 12kw per hour to keep it at21c when the external temp is -1
at the moment i am sitting here warm as toast and its now like this 24 hrs per day.

yesterday cost me 160 kwh of oil which at 0.45p is  approx 16 litres = £5.40  which is about right i would say
it would bee a lot cheaper with gas but i cant get it
if I had a ASHP working at a cop of 2 yesterday would roughly have cost 80kwh * £0.082 = £6.56 so I would hope to get a better COP than that.

I just wondered if you are trying for the impossible? its a big house and maybe you need to leave it on longer to do its job?

Mike

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