Navitron Renewable Energy and Sustainability Forum

HEAT PUMPS & Geothermal Energy => Heat Pumps => Topic started by: flip on December 29, 2010, 02:07:22 PM



Title: ASHP setup with rads and UFH
Post by: flip on December 29, 2010, 02:07:22 PM
I have a Delonghi AWR0031 MT 11.8Kw ASHP which feeds a 200 litre buffer tank which in turn feeds a ground floor with 5 zones on UFH and 1st floor and attic room with radiators.
It is currently setup to a return temp of 45 degC and I have a temp switch on the return flow of the buffer tank which will activate a grundfos pump when the temp is around 40 degC. Yes I know this is high for UFH but when I divert the water to the rads they are all but luke warm unless the ASHP is set up this way. The UFH downstairs makes the floor a comfortable 20 degC today and all the zones are off. The air source when this happens is off for a long period and thus saving us money.
For DHW we have solar and a immersion heater which comes on for 2 hours at night if needed to help raise water temp.
When I turn the rads on upstairs the pump then works harder and runs for longer periods.
I was wondering if anyone can advise on this setup, seems to be OK but I would really welcome some hints and tips.


Title: Re: ASHP setup with rads and UFH
Post by: Countrypaul on December 29, 2010, 03:51:25 PM
Is there just a single pump for both the UFH and the rads?
Does the water for the UFH go through a blending valve to use the returning water and thus minimise the use of fresh hot water from the store?

What you appear to describe is what some on here warn is the main problem with ASHPs, either you need UFH almost everywhere, or you need to get such hot water out of it that the COP ends up quite low.

When you use the immersion heater is this on E7?, do you run the ASHP on E7 when you can?

Paul


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on December 29, 2010, 04:02:33 PM
What you could do  is  have the  radiator circuit  use a higher take off point in the buffer tank and  use an immersion to boost only that section of the  tank in very cold weather.    This way you could keep the  output temperature  of the heat pump lower, particularly in cold weather,  when the heat pump would be  less efficient.    If the return from the radiators is at the bottom of the buffer tank  it would  increase  the underfloor  feed  temperature slightly.   Because upstairs radiators are  probably used mainly at night the immersion could use off peak electricity only.      

It is difficult to tell how much difference  to COP there is  when the output temperature  is higher.   The input air temperature makes an enormous difference.     I just set mine to the highest temperature  setting and let it  reach whatever temperature it can.   The electricity usage is the same  and a  higher temperature saves the immersion in the DHW cylinder.   When heating the buffer tank the first time  I   recorded the figures for the graph below.   Unfortunately   there was a heat dump from the  DHW cylinder in the afternoon, only a few kWh into the bottom of the tank,  but it upset  the  heat pump temperature control briefly.   What it shows is that once the ambient temperature is adequate there is virtually a straight line output  graph over quite a big  temperature range.


Title: Re: ASHP setup with rads and UFH
Post by: flip on December 29, 2010, 04:19:26 PM
Is there just a single pump for both the UFH and the rads? - no its one pump for the whole circuit

Does the water for the UFH go through a blending valve to use the returning water and thus minimise the use of fresh hot water from the store? not sure

When you use the immersion heater is this on E7?, do you run the ASHP on E7 when you can? not on eco 7



Title: Re: ASHP setup with rads and UFH
Post by: flip on December 29, 2010, 04:21:20 PM
If I set the pump to its max return of 45 degC would this be achievable in the very cold winters?


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on December 29, 2010, 04:52:46 PM
45C  might be just about possible if the outside air is  -15C  for example.  That is a rise of 60C,  mine  will only do about  50C rise but it has  a relatively small air throughput so it just cannot find enough input heat to work with.      If you are using the  full output  capacity  the temperature setting doesn't matter, you just let it reach what temperature it can  but if you have a choice it is better to drop the temperature setting a bit in very cold weather and boost heat by other means.   Although an immersion may seem a little wasteful to boost the temperature,  it  won't add up to all that much extra cost over the average year.   I just turned my heat pump off for the last two weeks  but now the average temperature is  22 degrees higher than last week and it has the buffer tank up to 53C.     


Title: Re: ASHP setup with rads and UFH
Post by: knighty on December 29, 2010, 11:35:56 PM
as a short term test.... can you turn your down stairs heating up a bit ?

the under floor heating will be much more efficient than your radiators, so by increasing the downstairs temperature, you could hopefully let the heat rise to the upstairs naturally and help heat it ? (might not work as planned, but worth a go?)

the only way to make the pump work less, without making any physical changes to the system is to turn the water temperature down


the colder the water temperature the more efficient the heat pump is (at generating heat)

but colder water makes the radiators less efficient (at dumping the heat into your rooms)


Title: Re: ASHP setup with rads and UFH
Post by: flip on December 30, 2010, 10:42:19 AM
Thanks for the advice, what I have done now is to put the heat pump to its max return temp of 45 degC. When the return hits a temp of 3 degC lower, in this case 42degC return the heat pump goes off. I have set the buffer to pump at around 40degC so at the moment the Grundfos pump will remain on all the time and ASHP will cycle, currently its off for 40min and on for 10min which is great (outside temp being 9degC now).

As for the UFH, I have left the hall stat fully open to heat rises and other 4 zones are set to 20 but have no call for water at this time.
We then put the rad upstairs on a timer to come on at night for 1 hour.

Seems to be working OK.
Main issue is when we get silly temps outside of -8degC etc.
I dont think the defrost cycle is correct, it starts to defrost at around -5degC and then goes into error, this is what messes it all up. The settings for this are only known by the company, not very user friendly pump!
Anyone know of Delonghi engineer settings for derfost?


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on December 30, 2010, 12:20:34 PM
It should need to defrost  when the ambient temperature is  above freezing,  the ice will build up due to  the cooling effect of the heat pump.     It is more likely that the intake being blocked by ice is causing the error. 


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 01, 2011, 02:49:35 PM
OK, I will contact supplier to see if they can change the settings.

I currently have Emmenti stats in each room controlling the UFH but find it a pain at night to turn them down in order not to waste heat. Does anyone of a stat that can be set to turn itself down at night, eg on timers etc, and can someone please give me a link to product.

thanks guys for your help so far


Title: Re: ASHP setup with rads and UFH
Post by: Baz on January 01, 2011, 10:49:40 PM
http://www.heatingcontrolsonline.co.uk/siemens-rdj10-programmable-room-thermostat-p-360.html
for example but a bit pricey for every room.
Do you want to turn them down or off? If they are plain 'stats that just go open circuit when hot enough you can just put a simple switch in series with the wires in a convenient place like at the boiler. That would give you a bank of switches for manual control. Starts to get more complex if you then want a timer to put them on/off but do-able with relays and a single timer.


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 23, 2011, 10:02:27 PM
I do not find the pump very efficent or capable during the cold temps of say minus 4 as it has been this week.
The default setting on my pump is a return flow of 45 degC and timer for upstairs rads to 8pm till 10pm. Think is when 8pm comes the pump struggles to warm the buffer tank up to make any differnence. To be honest I am thinking of getting rid of it, it may be eco friendly and all that but it simply don't work. Gas must be the better option surely?

The supplier says I could increase the return flow to as much as 55 degC, suppose this would at least make the rads warmer, but what effect does it have on UFH, it this temp too hot?
Any advice please or can anyone with a De-longhi pump give me feedback on theirs?


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on January 23, 2011, 10:47:06 PM
The idea of the buffer tank is that  you heat it before you need the heat,  normally this would be at night  in order to have heat in the morning.     The mixer valve on the UFH should mix the temperature down to  35C or whatever the setting is.  Of course you don't want to have to  heat  the water to 55C  and then have the mixing valve  reduce it by 20C   but  if the radiators need 55C then  you have to raise the setting.   In cold weather the heat pump probably won't  reach output temperatures above 40C.   

You need to have some way of boosting the temperature on occasions.   An immersion using off peak electricity  is  an option.   It would cut out on the thermostat if the heat pump reaches the target temperature.    In a normal winter  there is usually  only a total of a few weeks  with  below zero temperatures.


Title: Re: ASHP setup with rads and UFH
Post by: titan on January 23, 2011, 11:03:07 PM
The most efficient way to run this system is to have low temperature rads to keep keep the ashp flow temperatures as low as possible. Oversized normal rads are a compromise , proper low temperature rads should work fine. Low flow temperatures are the answer to effective ashp operation.


Title: Re: ASHP setup with rads and UFH
Post by: baker on January 23, 2011, 11:59:22 PM
Hi
sorry to hear of the problems
but it looks like a design problem
rads don't work  '@40c  as you now know
try fan coil rads  / java . go big
the defrost cycle is  temperature activated. and  timed to suit climate
could be a faulty sensor or reversion valve
does the heat pump auto re start after a set time?
is their any non return valves on Circe?


Title: Re: ASHP setup with rads and UFH
Post by: cornishben on January 24, 2011, 08:09:21 AM
ben taking notes...


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 24, 2011, 12:07:10 PM
In answer to some of your questions:

1. The pump will restart after 3 error codes automatically and then go off and require a manual restart, waiting for a response from supplier as to settings issue again. Problem here is that when we are in bed there is no way to tell if its on or off and results in a cold morning.
2. I understand that rads do not work good at 40 degC, but at the moment the buffer is set to pump water at 42 degC but when upstairs valves are open the heat pump struggles to get to this and keep the rads constant, this is why I wanted to boost the heat pump to at least try and get some hot water in there. With a return temp setting of 55 the pump will output 60, yes the ufh will regulate down to 45 but i think no other choice. I just can't believe I would need to consider a further booster to get the heat in there on a machine that cost around 4800 plus the 200 litre buffer and all the rest totals in around 6K plus labour.
3. If I were to set the timer on the buffer tank to be off through the night, so no flow out to UFH, only ASHP on, filling up buffer with hot water, I guess this would work, but is this not going to use lots of energy in the morning warming up the slab all over again? May be an option though. Scenario and suggested way forward:

a. set ASHP to 50 degC return temp to the buffer.
b. buffer timer to switch off grunfos pump at midnight and on at 5am to warm house in morning
c. remains on for rest of day until midnight cycle again
d. rads on at 8pm till 10pm upstairs

Is this the best way forward ignoring the defrost for now?
ANYONE WANT TO BUY IT? I'M GOING GAS, NOT SUITABLE FOR MY HOUSE ME THINKS. BUYER COLLECTS. WARRANTY RUNS OUT IN FEB. (2 YR OLD) OFFERS PLEASE.


Title: Re: ASHP setup with rads and UFH
Post by: baker on January 24, 2011, 03:09:39 PM
 HI
it looks like the buffer is the problem
if it can run down when the heat pump it on
what is the designed rest peroid for the heat pump
the buffed is designed for this peroid only
if the heat pump needs a manual restart
its not the start up secquence
maybe high limit /low pressure in sequence sensors
what part of the country are you in
i am sure it can be sorted / do you have the error codes and manual
send me email
john.eco4@gmail.com


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 24, 2011, 06:47:11 PM
The heat pump has a 3deg rest period, the time will change dependant on outside temp and other factors such as usage of hot water in buffer tank etc.
I have currentlly set the heat pump to work on a 50deg return temp, it goes into standby when it gets to this and comes back on at 47deg. However when it comes back on the temp does drop to around 46degC and then continues to go up again to 50degC.

The buffer has a temp switch on it clamped to the return pipe and I have set it to come on no less than 46degC so that my rads will get a good flow of hot water into them. Going to see how it goes but temps here in S.Wales at the mo are around 5 degC as I type this so defrost not so much an issue and i await contact from heat pump manufacturer to change these settings.

Will also try tonight timer to switch off the pump from the buffer and restart in morning at 5am to give us heat when we go to work.

Worth a try I guess.

ANYONE HAVE A DELONGHI ASHP??


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on January 24, 2011, 09:35:26 PM
You could start the pumparlier and  also start heating earlier  and try to get all the heating into the  off peak electricity rate.    As you say the floors, once warm, will keep downstairs warm all day and of course any sun through the windows will add to that.     To some extent heat from downstairs will filter upstairs  during the day.   

I try to have all underfloor circuits off by mid morning but the buffer tank can manage that with the pump off.   However since my heat pump only outputs 2-3kW   I have to also use it for a few hours in the afternoon, which is much more expensive,  so it costs two euro per day instead of one.    However by next winter most of the underfloor heat should come from the seasonal store.


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 25, 2011, 07:31:51 AM
What is the ideal pumping condition?
I currently have it set to:

1. ASHP on a return of 50degC to the buffer, goes off and back on at 47degC
2. Buffer pump switches on at 46degC

New timer settings are:
1. buffer tank pump on at 5am till 9am
2. again at 1pm till 10pm

Not sure if this is the way to go but trying it out.
Any comments?

I am not on Eco7 electric as does not work out for me to be worth it.


Title: Re: ASHP setup with rads and UFH
Post by: baker on January 25, 2011, 08:30:40 PM
if you cannot use economy 7  and have natural gas
fit a combi will work out better
your heat pump is designed for underfloor heating to run on eco7
for a home 200sqm approx
if you fit a combi and do the rads and dhw
hope this helps
regards
john
 


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 25, 2011, 10:05:05 PM
I have come to the conclusion that the ASHP will not heat my rads.
Tonight I turned off the UFH and turned on the rads to the first floor 8 in total.
Set ASHP to set point of 46 Deg C into the buffer and let rip.

As soon as the ASHP got to its max at 46 and turned to standby I watched it until it got to 44 and then activated buffer pump to send water to rads. At 43 the ASHP switched on as expected but failed in a 2 hour period to get to 46 again. Why is this, the temp outside is 7 deg C so the ASHP should be able to perform enough to get the temp to the rads only.

Are my buffer settings inadequate, what I am doing wrong here, or is the ASHP a load of shoit?
Getting frustrated now, lots of money spent here and wasted.


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on January 25, 2011, 10:13:30 PM
It is very hard to tell how much heat the  radiators are using.    The only way to check the  output of the  heat pump is to  cool the buffer tank,  turn off the radiators and underfloor heating  and then see how many degrise rise  per hour it can achieve.   


Title: Re: ASHP setup with rads and UFH
Post by: Baz on January 25, 2011, 11:46:44 PM
Went back to the beginning and see the pump is 11.8kw. You never said how big the place is but 2kw would boil most rooms after a few hours so that power must be enough for quite a few rooms, or it isn't giving anywhere near the output. What's the electricity consumption in eg the 2 hour period you mention?


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 26, 2011, 10:18:26 AM
when the pump is running output on the electric meter shows around 3Kw. Yes its a 11.8Kw machine, but it does DHW also but I do not use this function.
I agree it should be able to supply a couple of rads.


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on January 26, 2011, 10:36:59 AM
The actual  output in cold weather is probably closer to  6  kW.    It should be able to raise the temperature of the buffer tank  by about 25C per hour with no heat drawn off.      It it isn't able to achieve 6 kW output, or close to it,  then there is something wrong.       


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 26, 2011, 11:43:46 AM
yes it will raise the temp of the buffer quite easily with no heat output to rooms when the pump is off. this is what i have done:

1. switched off the buffer pump
2. let the ASHP get to the set point or return temp of 45 deg C it then goes off
3. it then begins to drop slowly to a 3 deg hysteris and when reaches 42 deg C it starts up again, I switch the buffer on when it gets to 44 deg C
4. As buffer begins to pump water into house the ASHP drops to 41 and can not get back up to 45 again

Please see my system below:



Title: Re: ASHP setup with rads and UFH
Post by: dhaslam on January 26, 2011, 12:10:16 PM
The time taken to  gain 3C  may not be a very precise  measurement because  it is only going to be  around ten minutes and  the full tank may not be heated by  3C.   You need to leave the heat pump off long enough to drop the temperature down  below 30C and then see how long it takes to come back up.      The reason why the  heat pump struggles around  44C is because  it's output reduces as  temperature  rises and also the output of the radiators goes up.   


Title: Re: ASHP setup with rads and UFH
Post by: flip on January 26, 2011, 12:35:15 PM
what setting would you recommend i put the buffer pump onto?


Title: Re: ASHP setup with rads and UFH
Post by: flip 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


Title: Re: ASHP setup with rads and UFH
Post by: Baz 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.


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam 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.       


Title: Re: ASHP setup with rads and UFH
Post by: flip 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?


Title: Re: ASHP setup with rads and UFH
Post by: flip 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??


Title: Re: ASHP setup with rads and UFH
Post by: Baz 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.


Title: Re: ASHP setup with rads and UFH
Post by: cornishben 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


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam 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?     


Title: Re: ASHP setup with rads and UFH
Post by: flip 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.


Title: Re: ASHP setup with rads and UFH
Post by: dhaslam 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. 

   


Title: Re: ASHP setup with rads and UFH
Post by: flip 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.


Title: Re: ASHP setup with rads and UFH
Post by: mpooley 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