He sent me this reply which I would like other people’s opinion about.
My house is too hot for my wife (not me ) the bills are low and the Cops are good so
I don’t think he is right at all !
I would love someone who has more knowledge than me to give an opinion please?
this is what he wrote
"Why do still think that the ashp is oversized?
During cold ambient you state the unit defrosted 13 times.
This shows that the unit is working too hard and need excessive defrosts.
Sounds like its running hard then defrosting then running hard then defrosting.
A classic symptom of undersizing.
The cycling of the unit is because you have the system set on weather dependant.
The flow temperature is set too low so easily achievable.
If the unit has a constant load it would run longer but slower giving
better control and reduced cycling and a warmer home.
Hello @mpooley can you share your heat pump dashboard link with the example of the 13 defrosts? sounds like a reasonable number to me but being able to see the data would help
I’m still very new to all this… Just pondering - to extract heat from air, you can either do a large temperature drop of a small volume of air, or a small temperature drop from a large volume of air. The former is likely to cause less frosting than the latter, since the air can only lose its water vapour once as it cools. (Though might also mean that the former would start frosting at a higher ambient temperature ?)
I’m not sure if that suggests that a smaller unit would tend to frost less than a larger unit ? (Assuming that the larger unit can pull through a larger volume of air.)
Thanks @mpooley looks pretty fine to me. Your sizing is probably fine, 6-7 kW accurate heat loss and 10 kW heat pump (probably a bit less real world max capacity) is about right IMO. E.g some of the best performing systems have that ratio.
Blockquote
I’m not sure if that suggests that a smaller unit would tend to frost less than a larger unit ? (Assuming that the larger unit can pull through a larger volume of air.)
Blockquote
I’d like to know the answer to that as well !
Thanks Trystan
It’s helpful to have someone look at the charts for me as although I have watched as many Youtube vids as possible and read a lot what about I should expect, looking at the charts is another level of understanding of what is is actually occurring and why?
I’m trying to understand what his argument actually is really I just don’t know enough about the inner workings of heatpumps I suppose!
Could you comment on his argument ? it sounds totally wrong to me . especially the bit about it being because I’m using weather compensation! the fujitsu Manual says that weather comp must be turned on
The frequency of defrosts is relatively high during periods where it’s running harder e.g a defrost every 30 mins. We do seem to see this higher frequency as a heat pump is operating closer to it’s maximum output. It looks like the 10 kW Fujitsu is a single fan unit, it may be that Fujitsu have tried to a pack a bit too much heat pump output into that evaporator size.
Some of the double fan 10 kW units e.g the Vaillant arotherm 10 kW seems to give better results when the heat demand is at a similar level. It might be that with the larger evaporator you get a smaller drop in the air temperature as it is pulled through the evaporator, (more evaporator surface area to heat extraction demand) and so frost build up will be slower.
You may get better results on the coldest days from the double fan 11 kW unit but then your overall performance across the year depends on how well that unit modulates down and cycles during milder conditions. If the 11 kW is actually the same compressor as the 16 kW unit which looks possible it may struggle to give good results during milder weather.
Can I share links to your dashboard directly here? I know your system is public on HeatpumpMonitor but not sure that you want to associate it to your name?
There is a bit of over cycling during some of the milder days, I think your weather comp minimum flow temperature might need to be a little higher. It seems to run nice and stable at 29.5C but it starts to cycle quite a bit when it tries to run below that as your hitting the minimum modulation of the unit.
There is a bit of over cycling during some of the milder days, I think your weather comp minimum flow temperature might need to be a little higher. It seems to run nice and stable at 29.5C but it starts to cycle quite a bit when it tries to run below that as your hitting the minimum modulation of the unit.
<
Following your comment I put the flow minimum setpoint to 30c last night I can’t tell from the chart if it’s altered much as My ISP changed at midnight and I didn’t have a network for a few hours!
The main difference is that its noticeably warmer in the house . I don’t see what I can do to drop the temps if the flow is at that level especially as today is much milder?
I seem to have a very unusual wife who does not like it above 20c! its about 23c at the moment.
if i change the weather compensation curve to compensate but the flow minimum is 30c what would be the effect?
Mike
) the bills are low and the Cops are good so
