akjos

Every heatpump needs about 2x to 2.5x the capacity of flow rate in l/min. so if you have a 6kw unit, about 12l/min. Make sure your system can achieve that and ypur zones are not closing.

Where did you get the 400l/hr from? As far as I know the heat pump needs a flow rate of about 2x to 2.5x the capacity. When it modulates, the compressor modulates to hit your target flow temp and the 5t delta, the flow rate of water does not change. But maybe the vaillant does it differently. Compressor modulation can go down to like 15-20% I think.

Found this manual on setting the WC curve on the Ecodan. Page 12: https://planetaklimata.com.ua/instr/Mitsubishi_Electric_PUHZ-W-HW_OPERATION_MANUAL_Eng.pdf

Your flow temp has been set by whoever installed/commissioned your system. Usually the setup is weather compensated, meaning you have a higher flow temp when it’s colder outside, and lower flow temp when it’s hotter. Heatpumps work more efficiently with lower flow temps, so you can expect a higher energy consumption during winter as the flow temps would be higher too most likely. Now in regards to heating your house, just ballparking it I still think 11kw should be enough for you. So it can either be as easy as bumping the flow temp higher, or there might be an inherent flaw with how the system was installed. Or your heat emmiters aren’t powerful enough to emit heat. Bumping the flow temp is easy. You just do it via the controller inside, though I dont how how exactly on the Ecodan. Other people on this forum will know or a google search will help you figure it out too. Just bump the weather compensation curve up, i.e higher flow temps and see what happens. That’s the easiest thing without any changes to the system, but your efficiency will drop a little.

What’s your calculated heat loss and what’s your HP capacity? Also, UFH or rads and what flow temperature are you running?

If I remember correctly, manufacturers need to publish data at 7’C outdoor temp and 35’C flow temp. That’s where the unit produces the label output… Quite stupid tbh, as nobody designs at those numbers. So always check the detailed tech spec. Also keep in mind that during defrost situations (~4’C outdoor temp) the unit looses an additional 10%. It kinda has a dip in its capacity curve, which they rarely document.

In cooling the heatpump will run the refrigerant in reverse in a way and dump heat outside while cooling your water in the heat-exchanger. You can then use the cool water for cooling. UFH is better suited for this as the surface area is large. With radiators you might not see a big difference. The most important thing is not cooling the water below your dew point as then you will have condensation on your pipes and potentially horrible water damage (mold, rot…). So always see what your dew point is (calculate it with your relative humidity and temperature) and run the water above that. From what i see in the Yutaki documentation, it can cool the water to 7’C degrees. You will also need the additional cooling accessory kit, but I think that’s just an electrical pin which activates the function. A better way to cool if you don’t have UFH is to pipe an additional water pipe with a zone valve to a fancoil unit installed in the rooms you want to cool. The fancoil unit cools the air with the cool water from your HP and blows it into your room. It also has a condensate drain, and you can use it for heating too if you wanted to.

@rhymecheat did you get to the bottom of this? Interested in what the issues were. Thanks.

@LA3222 how did you go about calculating W/m2 for the UFH for both ground and first floor (if going from a known total amount of fabric heat loss)? You obvs have a very tight house with minimal losses, but did you just divide the total heat loss by the total floor area (ground + first floor)? My estimated heat loss on slab and ceiling will be roughly the same, so both floors balance out, but my confusion comes from the fact that not the whole floor area has losses both up and down. I'm trying to figure this out now in order to calculate the spacing/flow rates so that I can run an ASHP most efficiently 24/7 without any buffers. Thanks!

@willbish are you running your UFH directly from the ASHP water pump? If so, any issues so far? And also do you know how the ASHP actually controls the pump? I’m planning a similar simple system. Monobloc ASHP directly feeding UFH from internal pump without any buffer, zones or thermostat. Whole system one zone and weather compensated based on heat loss of the property (and also a three port valve for DHW but that’s standard). thanks