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26-02-2010, 09:47 PM #1
Altherma frequent compressor cycling
Hi!
I'm a new member here, so I would like to say hello to everyone first! I hope you can cope up with my writing since I'm not a native English speaker.
I have a new house with a 6kW of heating power needed at -10°C ambient temperature, heated by an Daikin Altherma 8kW model (using Daikins swing compressor), driving a combination of underfloor heating and oversized radiators (connected on the same loop and using the same water temperature as the underfloor heating, always below 35°C ). I have no buffer tank. Indoor temperature regulation is done using Altherma's weather dependent water set point.
Altherma can regulate heating power from 4kW to 8kW. House needs 4kW at 0°C outside, so at higher outside temperatures (like these days as it is 7°C to 10°C outside) it has to work in intervals. Here comes the problem with cycling :
- altherma switches on for 2 minutes, starting with an higher compressor frequency and then gradualy reducing it, unitl it switches off at the end of this 2 minutes interval (since there is not enough heat demand).
- it waits for 2 minutes (nothing is running, not even circulation pump)
- switches on only the circulation pump for 2 minutes to read the water temperature - it is cold enough to cause it to start the compressor and starts the cycle again.
So I have a compressor start every 6 minutes - it means 10 in an hour -> more than 200 per day!
I believe that such a number of compressor starts is a recipe for heatpump failure, not to mention that it makes it difficult to maintain constant indoor temperature.
I guess I could install an indoor temperature thermostat but I would prefer not to do it, because of the slow response from underfloor heating and low house temperature inertion (it is made of light prefabricated insulated elements) - it means that at quick outside temperature variations the indoor temperature would lag behind. Maybe a buffer tank would help but I have no space reserved for it (water unit is located under the staircase). I found no way to reduce the number of cycles using user modifyable settings.
Is anyone else experiencing such problems with frequent starts/stops? Or am I just making an elephant out of a fly? Can a swing compressor withstand such a frequent cycling? I guess the same goes for pipes and heat excangers - is there a chance of early failure because of frequent pressure cycles? It is our first "real" heating season, heat pump was installed a year before (nov 2008), but rarely used since the house was not finished inside and we did not move in. I have another year of 3 year warranty period. I hope it does not break down the next day warranty expires. Can it last 10 years with such working regime?
Kind regards
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