View Full Version : Daikin Altherma HT: Room vs Exit Temperature

02-02-2015, 12:41 PM
Hi Everyone,

I have just purchased Daikin Altherma HT. And, currently using the room thermostat to set the room temperature to 23 Celcius. But, it looks like it is taking forever to reach something like 23.5 and then it shuts itself down for ~ 1-2 hrs till temperature drops to 22.5 (or 22.7, cannot remember it exactly now), and takes another 2-3 hours to reach 23.5. And, in the meantime, it looks like it is consuming a ton of electricity.

So, I was wondering, whether it is a better idea to set exit temperature to something like 45-50 at a fixed rate and keep it like that when I home and 5-10 degrees less when we are not at home. Do you think it would be more efficient like this?

Basically, what is the most efficient way is what I am trying to ask...


02-02-2015, 01:51 PM
Presumably the Daikin HT is supplying hot water to your radiators? Is your house a new build or just a boiler changeover onto existing radiators?
If the temperature in your house takes 1-2 hours to drop only 1 DegC, then your house must be very well insulated, however if the system then takes a considerable time to bring the house back up to temperature, this suggests either your radiators are not balanced properly to provide the correct amount of heat output and delta T at the Altherma, or the thermostat is in a 'dead spot' and not registering the change in the temperature, or possibly your thermostat may be out of calibration.
Normally the most economical way of running the system would be to let the Altherma determine the water flow temperature dependant on changes in the outdoor ambient temperature and then control the temperature of the living space with a programmable thermostat to give you the facility for temperature set back when the house is not occupied.
If you have normal sized radiators and have set the water flow temperature too low, then the building heat up time will be extended considerably.

02-02-2015, 02:16 PM

Thanks for the quick reply.

We have converted an existing system and we are using regular radiators. Insulation at home is not great, but it is definitely better than average (has double bricks with foam in between).

I am really baffled by this. The thermostat is in our living room and it is in line with the regular thermometer I have in our living room (at most + / - 0.3 or so). And, also added some foam padding (between thermostat and wall) so that it won't get affected from the wall. We also thought that radiators there were not enough and have added more radiators. And, whenever I look at water exit temperature, it is around 55 (set to auto).

And, looking at the consumption, it is quite high with this setup. And, I was thinking if I set the exit temp to 45 or so and leave it on all the time, it might be more optimal.

BTW, what is the start / stop range for the thermostat? As far as I remember, it was stopping at + 0.5C and starting at - 0.3C ? Is that correct?


30-04-2015, 01:48 AM
HiGuess "heating season" is over for this time... but.That how it works... you set 23*C it will work until it will reach 23,5*C and stops .Starts again when temp drops to 22,5*CIf it's hard to reach desired temp in the house, then you must simply increase the out temp setting.What I learned is that it's more efficient to have the temp setting ( on water out ) just about high enough to reach 23,5*C. The Pump will then keep 23*C or so... will work most of the day... but with less effort...Min required temperature out, so this way it's more efficient.You have to try it out... set your curve say 45*C when its 15*C outside..and 65*C when it's -20*C...Observe and adjust ( need to have the weather dependent function on though ).Now I don't know what temp you experience in your area.... and what temp your radiators are designed to work withNote that +15*C outside then 45*C on the radiator water and -20*C outside and 65*C radiator water is just a setting... in order to create a curve the pump will follow when outside temp changes.This can be different for different houses in different climates.Good luck.

30-04-2015, 01:47 PM
How have you connected your room stat to the Altherma?

08-05-2015, 04:59 PM

The control panel with room temp sensor is located in the living room.
Wired to the rest of the unit... ( indoor unit is in a utility room ).

But I think I know what you're aiming at....( may be wrong though ) :)

Some people may have the controller in the same room as the unit, i.e actual
temp achieved in the house will not be considered vs the temp setting...