Sizing Low temperature rads for Daikin Altherma

[Debonair Spain]

Hi all, i would like some info on the calculation to size low temp rads ( Jaga ) to a Daikin Altherma.

I am sizing a house at the moment in Spain, i am familiar with heat loss calcs but with flow temperatures of 55 and a return of 45, are the calculations different.

For example i have a room with a heatloss of 2100watts, now the rads required would be 2 X 1050watts and the physical size of these are 1.2 meters long. But a heating company has given me their calculations based on surface area X 115w psm and their heatloss calc is more or less the same as mine but they have given me 2 X 788watt low temp rads, which is 600 watts short for the room.

Now i know Low temp rads convect the heat but does that have any bearing on the output of the rad.

I look forward to any replies.

Debonair Spain

[nike123]

They should be almost double in size than normal radiators for 75/65°C temperatures.
So radiators for your system should have catalog power output (75/65°C) of about 2100W to get 1050W at 55/45°C temperatures.
Why not use fan-coils? They have much better temperature distribution and better suited for low temperature aplication.

[Debonair Spain]

Hi Nike123 thanks for the quick reply fan coils is not an option because the people prefer central heating.

I just cannot understand why the heating supplier of the Jaga rads has undersized the whole house.

I will need to consult further before i submit a price.

Many thanks

[Debonair Spain]

Hi all i would appreciate some more comments please.

[Brian_UK]

Is it too late to fit underfloor heating to take advantage of the lower temperature available?

edit: Some data relating to the change of radiator sizes is given in this papr....

http://www.mas.bg.ac.yu/istrazivanje/biblioteka/publikacije/Transactions_FME/Volume35/3/3.%20Banjac_129-134.pdf

However, I believe your figures are correct, whatever the radiator is it still needs to output the required design heat loss.

[Debonair Spain]

Hi Brian thanks for your reply, they were considering underfloor heating and i did suggest that the Altherma would work better with this system
But as usual money if a factor and it would mean concreting and tiling the whole house, which would put the price up considerably.

[multisync]

When we were all down there, I'm sure the chain smoker said any rads would only need to be 20% bigger...?

[multisync]

Hi Nike123 thanks for the quick reply fan coils is not an option because the people prefer central heating.

I just cannot understand why the heating supplier of the Jaga rads has undersized the whole house.

I will need to consult further before i submit a price.

Many thanks

I know it is Spain but when I had a quote for a new CH system they sized on much lower temps than the Mrs would accept. IE 17 ideg C in the hall bedrooms etc.

[Debonair Spain]

Hi all yes i believe Multisync could well be right that the Spanish size to 17 degrees c which is not good for the times when you really need it especially when their houses have a tremendous heatloss.

Thanks for all your help, this site has a wealth of knowledge.

[brunstar]

try visiting www.altherma.co.uk (http://www.altherma.co.uk/)