@huwsy in which case you've really been done over by them. You should ask them for their heat loss calcs in the first instance, try the methods suggested in this thread to get a bit better performance, and then look what paths for recourse you have with your installer. Have you already told them the system is no where near adequate? Are they MCS accredited?

Hi

They are MCS accredit and it’s plastered all over their website, but only for air to water installs not, as we have found out, for air to air.

I have started measuring up for the MCS spreadsheet of heat loss and it already doesn’t look promising for our inverter at only half way through the house. 

Thanks

Posted by: @huwsy

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We stipulated to our installer that we needed 24-26C out of medical necessity, sever risk to life

I hope you put that in writing and wish you luck with getting a resolution.

Posted by: @huwsy

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Hi

Thanks both, Setting lower temps like 22C knowing it doesn’t achieve 22C when set at 30C seems counter intuitive but I will retry in the next cold snap on high fan speeds and lower room temps.

Out of interest should these or air to water ever be able to get to 25/26C within rooms over winter or is that too high to achieve as most things I see are for around 21/22C

The home is only slightly above average size but solid stone dating early 1800s amongst other designs ideas from the time so the heat loss isn’t great. 

Thanks

It is merely a matter of balance between the amount of heat energy supplied and the amount of heat energy lost.

If the heat loss of your home is say 15kW, at an inside temperature of 21C and an outside temperature of -3C, then your heating device will need to provide 15kW of heat energy to keep the inside temperature at this level. If you wish to increase the indoor temperature to 25C, then the heat loss will now be in the region of 17.5kW, so that is now the amount of heat energy that the heating device will now need to supply to raise the indoor temperature to 25C.

If in the above example the maximum heat energy output from the heating device is 16kW, then the maximum achievable indoor temperature would be approximately 22.6C. If the outdoor temperature now falls from -3C to -5C, then the maximum indoor temperature will be in the order of 20.6C.

An A2A heat pump should be more able to raise the indoor temperature higher than the standard 21C, because it does not suffer from all the restrictions of an A2W system.

Do you require a indoor temperature of 25C throughout your whole home, or just in selected areas? If it is the latter, then turn down the temperature setting in the areas where the higher temperature is not required, which may divert some additional heat energy to the areas which do require the higher temperature.

Using a heat loss calculator, check to see if the fan units in the higher temperature area are actually of adequate size to meet the heat loss at this higher indoor temperature. When carrying out the heat loss calculation don't forget to use the lowest expected outdoor temperature.

If, as I suspect, your heating device may prove to be inadequate for your needs you have a number of options.

1) You can use an electric fan heater, or similar heating device, to raise the indoor temperature to the required 25C, in the areas in question. But only when necessary because of low outdoor temperatures.

2) You can improve draft proofing  and insulation levels to lower the heat loss. A more cost effective solution in the longer term.

3) You can install additional A2A heat pump capacity in the areas where the higher temperatures are required. You may need planning permission to install extra outdoor heat pump units.

Hi

Annoyingly the temperature was a strict requirement, as was a few other medical points, and the contract has the others but nothing on temperatures.

Having used the MCS spreadsheet and spending the morning measuring all the oddities in the roof and walls I have got a 21.25kW heat loss/requirement before even looking above 21C. So the 13.5kW was never going to cope. I’m surprised it didn’t pack up completely under that disparity. 

We require 24-26C in at least 2 rooms at all times, however we have discovered the Fujitsu setup installed doesn’t shut off valves to individual units so even leaving 4 units turned off and 2 set to heat the 4 off still warm up to 50C internally under the air filter they just don’t spin the fan so we don’t seem to be able to get more load to just some units effectively. 

Given we are facing issues getting to temperature even in autumn I think I’ll have a go playing with the insulation in the spreadsheet to see which things I can insulate to get nearer to the mark without costing a small fortune. 

Thanks

@huwsy you should have looked at daikin for this system, their vrf technology is better suited to running different rooms at different temperatures.

Posted by: @huwsy

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We stipulated to our installer that we needed 24-26C out of medical necessity, sever[e] risk to life...

Annoyingly the temperature was a strict requirement, as was a few other medical points

24-26 degrees is a very high medical requirement. The evidence is far from perfect, but the findings suggest a minimum of 18 degrees, even for older people with chronic illness, and that temperatures up to 21 degrees 'may be beneficial'.  A tolerably competent review of the literature by Public Health England in 2014 can be read here (<=link).

If the requirement for 24-26 degrees was a strict requirement out of medical necessity, because of severe risk to life, it would have been a good idea (to say the least) to write it into the contract in black and white terms, such that if the temps weren't reached, then a breach of contract would occur, with all the usual remedies. That said, contracts can be verbal as well as written, but the problem with verbal contracts is that all too often they can't be proven to have occurred. But if it were me, I would be asking my medical adviser why I needed such high indoor temps, all the more so given the recent astronomical increases in the price of energy. I would want to see chapter and verse on how those temps came to be recommended. There's no point in staying warm only to die of starvation, because you have no money left for food!

PS no need to disclose any medical info, of course, and the above is only a general recommendation intended for anyone who has been given a high indoor temp recommended on medical grounds.     

Hi

Our installer mostly deals with Daikin equipment, I had mentioned to them Mitsubishi equipment as they have a vrf equivalent but they decided Fujitsu and I wrongly assumed they knew what they were doing not just getting the cheapest things for themselves or what ever other basis they may have used to decide. 

As for temperatures, this is both medical advice and first hand experience in the household and has made us look at emigrating several times previously. 

Could being underpowered cause it to defrost more regularly? Or would the hourly defrost be normal for the subzero temps and the underpowered just means it can’t raise enough temperature each heating cycle to compensate for the defrost?

Thanks

Installers understandably enough tend to have favoured brands, familiarity and all that, but a good one will readily consider another brand if it is more suitable. A discussion with an installer about why they both favour their chosen brand and what they think about other brands and why, and whether they are prepared to be flexible, is I would suggest a useful thing to do when short-listing installers.

Emigration is certainly one way of escaping our cold damp climate, often the damp is as detrimental to health as the cold. You certainly wouldn't be the first Brits to have solved the problem that way if you did do it. You would also cure all traces of lingering HPDHD (heat pump deficit hyperactivity disorder).

"Could being underpowered cause it to defrost more regularly?" Possibly, as it will be working harder. But the main determinant of defrosting is ambient temp and humidity. Recovery from defrost is often poor, many members here on the forum have documented the phenomenon. Low ambient temps really are the Achilles heel of British heat pump installations, everything goes pear shaped. I wonder how countries with colder climates manage their heat pumps? Is there a better way of preventing or managing frosting? Or is it a reflection of our cold damp climate?   

@cathoderay once you get below -5 there is no moisture in the air so you get substantially less defrosting - nothing to freeze. I used to live in Finland for a bit and -10 feels better than -2.

Hi

So being cold but not often sub -5C and in eyesight of the sea with a 80%+ normal humidity is not a good place to be then. I’ll just try moving the house… haha

Thanks

@huwsy its just the humidity that will get you. Only thing you can do is tweak down the flow temps so the unit doesn't freeze as often.