sizing of air-towater heat pump

[axsaxoman]

Hi,
looking for advice +also checking if people are telling "porkies"

I have a well insulated wood framed house built 1979+loads of extra insulation +new double glazing
floor area 1000sq feet (total for both floors)
underfloor heating
what size of unit to replace an aging lpg baxi bermuda .
I also have a 300litre s/s tank-double insulated with kingspan kooltherm sections
tank has 3 internal coils
underfloor
hot water
solar (40thermomax tubes)
parent volume of tank is heated by the baxi at present

I am being told that a 5kw unit will replace the 28kw lpg unit.
can give me some unbiased advice please.


and when you want to supercharge or turbo your car or fit a stand alone ecu--i will give you all the tech help you need
(i work with a different type of heat pump)

[RSTC]

How was the 28 kW coping with the load? All things being equal it would want to be only running at least a fifth of the time to be considering it as a replacement. (ie if it's snowing outside and you can hear the burner running constantly then you need 28kW regardless of how you produce it)

[axsaxoman]

no the baxi is never running for that long at a time--even last winter when it was -15c
it was kicking in every hour or so for 10mins--

[desA]

no the baxi is never running for that long at a time--even last winter when it was -15c
it was kicking in every hour or so for 10mins--

You may want to check the discharge capacity of the heat-pump with outside air at -15'C.

Also, the amount of defrost time taken per hour may influence your final selection significantly.

What delivery temp do you require?

[frank]

Has anyone done a heat loss calculation on the house?

Any type of heater must equal or exceed the heat loss to be of any use.

Without numbers, it is difficult to give advice.

[axsaxoman]

delivery temp will be around 45-50c as i have underfloor heating and I have all rooms on individual timers+stats with zone valves.
Yes i have had a calculation done and the suggested gas boiler replacment was a 18-23kw --
What I,m really trying to get at is the total mismatch in kw ratings of heat pumps to boilers.
I just don,t want to end up with a heat pump that is too marginal and at same time I understand that these units are better running for a good time period rather than short on /off cycling ,which i would imagine is what would happen if i choose too large a unit .
.
heat claculations say use a 8.5kw heat pump ,but due to my large tank 300litres+the solar panels I am being suggested that a 5kw ecodan will be fine .
I understand your point regarding it being hard to give advice without numbers ,but even heat claculations work on alot of assumptions and not empirical facts--.

I get exactly same silly questions in my biz --performance tuniing -specialising in super+turbo charging+ stand alone euc,s , and without a dyno run to start with to get base line data its hard ,
but by the same token ,if you ask me what boost+ what charger unit to use to give 300bhp on a certain engine i can get pretty close at first guess.
-15c is not normal winter temp --exceptional --usually hovers around +3 to -3 most winters

[axsaxoman]

How was the 28 kW coping with the load? All things being equal it would want to be only running at least a fifth of the time to be considering it as a replacement. (ie if it's snowing outside and you can hear the burner running constantly then you need 28kW regardless of how you produce it)

I live in SW scotland near stranrear ,so climate is very similar to belfast

[RSTC]

Hi Axsaxoman (did you say that name out loud before you picked it?) In overly simple terms if 28kW runs for 10 mins in the hour then 5kW is going to be knife edge close.

The solar panel may reduce your running costs but not your required load (it only works when the sun shines!)

The tank will give better run time but again not affect max load.

In car terms if you're taking out a 2.5litre diesel engine and putting in a 1.4 petrol into the same car what is going to happen? I'm not saying for a moment that it won't work, but do consider that it will need to run consistently in cool weather.
H

[frank]

If you register here you can download the Daikin Altherma sizing tool www.extranet.daikin.co.uk (http://www.refrigeration-engineer.com/forums/www.extranet.daikin.co.uk)

What you will need is the floor area of the property and the calculated heat loss

[axsaxoman]

thank you ,I have done that and am now looking at a daiken altherma 8.5kw unit