MVHR - Geothermal Brine Heat Exchanger

[pdf27]

11 hours ago, JSHarris said:

 

Essentially it's a very, very dodgy area in the UK climate.  The reasons are to do with keeping the ground heat exchange ducts free from mould and fungal growth for decades.  At least one house in Belgium has been made uninhabitable by a poor choice of duct for their MVHR (worth a read): https://www.greenbuildingadvisor.com/article/belgian-passivhaus-is-rendered-uninhabitable-by-bad-indoor-air

 

There are a couple of companies that offer silver-coated ground ducts, to try and prevent mould growth, but they are expensive and (as a scientist) I'm no convinced of their long term reliability.  I personally like "permanent" house systems to have a life of several decades, as the last thing I want to do is have to dig up an established garden a few years later.

http://passivehousepa.blogspot.com/2012/12/earth-tubes-heating-and-air.html is worth a read on this - they've used corrugated PVC pipe which is slit at the bottom, which provided they're above the water table means that condensate will immediately drain out of the pipe. Instinctively that's a far better way of approaching the problem for me than silver coating, sumps, etc.

 

In any case, people really need to have a think about what one of these units actually does before getting too excited about what it does. It's essentially a very high COP preheater for the MVHR - which itself is a 90+% efficient heat exchanger. So the biggest single impact of fitting one is that it will significantly increase the temperature at which your MVHR discharges air to the outside world. In colder countries this is actually worth quite a bit since it eliminates the need for a defrost heater on the MVHR, but in the UK climate the power used by one is trivially small so not worth worrying about. If you're only using it in winter for pre-warming air, of course, you won't have any mould issues due to the lack of condensation.

That just leaves the summer cooling/dehumidification. Problem is, at normal ventilation rates it doesn't actually provide very much cooling at all - and increasing the flow rates requires a much larger/longer tube than you would otherwise need for the same impact. Compare the price of an earth tube with that of an extra PV panel which would provide the power for quite a bit more cooling, and I think the maths is pretty clearly against it.

 

10 hours ago, JSHarris said:

Yes, definitely.  It only makes sense for us to use an ASHP because we stuck with only having electricity, plus we have a fair bit of PV, so summer cooling using the ASHP is almost always "free",

 

You just need to weigh up the capital cost of the brine loop cooling versus it's effectiveness, which is unlikely to be very good.  You may want to consider a cheap air-to-air heat pump to address cooling, as opening windows won't help at all when the outside air temperature is warmer than your desired room temperature.  Air-to-air heat pumps are pretty cheap and if designed needn't cost a lot to install.

Actually, I'm not convinced by that: if we take an average-ish UK house (100m²) insulated to Passivhaus standards, it will need ~1500 kWh/year of heat and going by the Clark/Grant paper ~3,000 kWh/year of hot water. That would take 5,000 kWh/year of gas or roughly 1500 kWh/year of electricity (varies with a number of factors like air temperature). That's £284/year for gas or ~£250 for electricity going by the fuel cost values in SAP10: essentially no difference in running cost. Gas is cheaper for bigger or higher consumption houses, but the standing charge starts to hit you very badly in small or very well insulated houses. If you have PV and use the Smart Grid functionality on the heat pump, then the break-even size of the house with gas is likely to go up a lot due to the dominance of hot water in the total requirements.

The difference in capital cost between a gas boiler or a small ASHP is also pretty small - particularly for monobloc units which are probably easier than a gas boiler to fit and mean there is no need for mucking about arranging for a gas connection to be moved. IMHO, this means that if you have a cooling requirement then ASHPs probably beat mains gas for any properly insulated structure that isn't stupidly big, and even if you don't think you'll ever need cooling they're probably worth considering for any house below about 150m², more if you have PV.

 

We're planning to rebuild our current house and replace it with something at about Passivhaus standard of around 180m², and despite the fact that we're on mains gas at the moment we're planning to shift to heat pump only with no gas connection. This is largely driven by the desire to have some sort of cooling (my wife is from the USA and grew up with air conditioning, so hates heatwaves here). I've been playing around with the numbers for a while and I really can't get anything other than a small ASHP to work - the requirement for a second system to provide and distribute the cooling if we try any other way of doing it is just a killer for the economics.

[newhome]

I’m not on gas here so moving to an ASHP from my current electric boiler and non working solar thermal seemed to be a no brainer. The RHI scheme seemed to be a decent way to go for a property of this size but despite contacting quite a few installers I have only managed to get 1 quote which is for an 11.2kw monobloc and 300l UVC. It comes in at 14.5k. Even with the RHI I can’t make the numbers stack up and it seems cheaper to stay on electric. My biggest fear however is not having any support when it needs to be serviced. This is the reason the ST lies broken. An approved installer was paid 2.5k to fit it (installation only) and he won’t come and service it as he ‘no longer fits them’ and I can’t find anyone else to come. If I had gas here I would choose a gas boiler over an ASHP simply because the more mainstream nature means that finding someone to fix or service it should be easy. With the RHI scheme not allowing any backup heating unless on a metering for payment system that I wanted to avoid I could be stuck without heat for a very long time before I found someone to come. The RHI scheme does not even allow ST to be used for space heating alongside an ASHP without using a meter for payment which I find nonsensical. 

[ProDave]

^^ The parts cost for that system are likely to be in the order of £5K so that is a HUGE installation cost, confirming my opinion of the MCS rip off scam.

[Jeremy Harris]

@pdf27.

 

Depends who's figures you choose to believe for COP, and with the greatest respect to Nick Grant, he has always looked on the optimistic side with regard to alternatives to burning stuff (particularly wood and biomass, hence that bloody great rift in the AECB a few years ago), and is a strong supporter of heat pumps (as am I, come to that)

 

I'm inclined to the view that it's "possible" to get a COP that averages above about 3 for a carefully tuned and set up ASHP that is never called upon to deliver DHW.  In fact I'd go further, and say that based on our personal experience with a carefully tweaked ASHP we can average an SPFH2 of over 3.5 all year around.  However, there is a fair bit of contradictory evidence from the EST and anecdotal evidence from members here, that getting an average COP of even as high as 3 throughout the year is not common (I don't think there are many here that are measuring true SPF in any meaningful way).

 

There's no doubt that the competence of ASHP installers seems to be improving, and I believe, based on my own experience, that it is that which is having far and away the most significant performance improvement.  I also think we need to stop looking at heat pumps in terms of COP, as that's a deeply flawed measurement that takes no account of defrost cycling, resistance boost heating within the heat pump itself etc, and I think we should really be talking in terms of SPFH2, rather than COP, as a more balanced and accurate measure of energy in versus energy out over the whole year. 

 

The latest government data set is, by it's own admission, flawed, with lots of variability as a consequence of inconsistent measurement methods, but it does seem to indicate that a minority of ASHP installation reach or exceed an SPFH2 of 3, Only around 21% or so of ASHP installations exceeded an SPFH2 of 3.0,  and there are a still large percentage of installations that are below an SPFH2 of 3, which does still just make gas a better bet at the moment (part of this may be that the government target SPFH" is only 2.5 - so few installers try to get better performance than this, perhaps. 

 

The worst case is the one Nick Grant and Alan Clark have highlighted, where there is a relatively high DHW demand, a condition where all heat pumps start to suffer from performance degradation due to the relatively high Δt.  ASHPs using CO₂ as the refrigerant may improve things, and reduce the scope for installer set-up induced variations, but right now we at a point where if someone just gets an ASHP installed by a random installer the chances are that their SPFH2 will be lower than 3, making gas both cheaper and lower in terms of CO₂ emissions.

 

There's every indication that heat pumps. or more accurately their installation and setup, will improve in the next few years and the plots below are likely to shift to the right, but I think we are a way off that point yet, as change only seems to happen very slowly, unfortunately.

 

 

[newhome]

13 minutes ago, ProDave said:

^^ The parts cost for that system are likely to be in the order of £5K so that is a HUGE installation cost, confirming my opinion of the MCS rip off scam.

 

It’s all a rip off here which is what I told the lady from the Energy Saving Trust when she came to visit. She herself said that numerous people had told them that they couldn’t get installations for ASHPs from suppliers in Scotland and they were suggesting contacting installers in England. She said that in her experience installs started at 9–10k for the smallest ASHPs so she wasn’t surprised to see that mine was 14.5k. At that price it ain’t gonna happen! If anyone wants a career change there’s one right here to consider!  

[Jeremy Harris]

The cheapest supply and install price I was quoted for a very small and simple monoblock ASHP was around £5k to £6k, IIRC.  I bought a unit for £1700 and installed it myself in around half a day.  The installation parts probably added another £100, and I'd already concreted in some concrete blocks on their side to form the two raised mounting piers the unit needed.  The hardest part was carrying the ASHP around to the back of the house and lifting it up onto the concrete blocks. 

 

I did spend a fair bit of time reverse engineering the controls, working out how to get it to run in cooling mode and tweaking the settings to improve the performance, but none of that would have been done by a normal installer, I'm sure.

[Dreadnaught]

1 minute ago, JSHarris said:

I bought a unit for £1700 and installed it myself in around half a day.

 

@JSHarris is yours a monoblock?

[ProDave]

6 hours ago, newhome said:

 

It’s all a rip off here which is what I told the lady from the Energy Saving Trust when she came to visit. She herself said that numerous people had told them that they couldn’t get installations for ASHPs from suppliers in Scotland and they were suggesting contacting installers in England. She said that in her experience installs started at 9–10k for the smallest ASHPs so she wasn’t surprised to see that mine was 14.5k. At that price it ain’t gonna happen! If anyone wants a career change there’s one right here to consider!  

My 5KW heat pump would have been a little over £2K if I had paid full list price, so with a 300L tank as well, £3K for parts. Lets add another £500 for pipe, fittings and controls so a total cost of £3.5K

 

So if an installed price starts at £9K, someone is charging £5.5K to install it.  Lets be generous and say the plumber gets paid £300 per day, that's 18 man days of labour you are paying for, and it is not going to take anything like that.

 

SOMEONE is making a LOT of profit out of that job.  I have long suspected that MCS installers deliberately inflate the price, to just about the level of RHI payments you will will get, so it is not YOU the customer benefiting from RHI, but the installer who gets away with inflated prices.

 

I really think the government should investigate the high MCS prices.  Failure to do so suggests they are happy for most of the RHI payments to go straight into the pocket of MCS installers, rather than benefiting the customer.

[Jeremy Harris]

Just now, Dreadnaught said:

 

@JSHarris is yours a monoblock?

 

Yes, it's a Carrier 30AWH. the 6/7kW model, badged as if it were made by Glowworm.

[newhome]

5 minutes ago, ProDave said:

SOMEONE is making a LOT of profit out of that job.  I have long suspected that MCS installers deliberately inflate the price, to just about the level of RHI payments you will will get, so it is not YOU the customer benefiting from RHI, but the installer who gets away with inflated prices.

 

The max RHI I would get would be 9.1k over 7 years. If I could get the install at around 9k I might go for it even if that’s still considered to be quite a lot for the installation, but I’m not paying 14.5. That quote wouldn’t work with my current heating tariff anyway. 

 

I imagine some of the companies are larger and have more overheads but even so it’s too expensive in my view. 

 

Someone mentioned a scheme when companies installed ‘free’ ASHPs in return for handing over the RHI payments. Not sure that’s something I want to consider however and I haven’t yet read the small print. 

[pdf27]

3 hours ago, JSHarris said:

There's no doubt that the competence of ASHP installers seems to be improving, and I believe, based on my own experience, that it is that which is having far and away the most significant performance improvement.  I also think we need to stop looking at heat pumps in terms of COP, as that's a deeply flawed measurement that takes no account of defrost cycling, resistance boost heating within the heat pump itself etc, and I think we should really be talking in terms of SPFH2, rather than COP, as a more balanced and accurate measure of energy in versus energy out over the whole year. 

 

The latest government data set is, by it's own admission, flawed, with lots of variability as a consequence of inconsistent measurement methods, but it does seem to indicate that a minority of ASHP installation reach or exceed an SPFH2 of 3, Only around 21% or so of ASHP installations exceeded an SPFH2 of 3.0,  and there are a still large percentage of installations that are below an SPFH2 of 3, which does still just make gas a better bet at the moment (part of this may be that the government target SPFH" is only 2.5 - so few installers try to get better performance than this, perhaps. 

 

The worst case is the one Nick Grant and Alan Clark have highlighted, where there is a relatively high DHW demand, a condition where all heat pumps start to suffer from performance degradation due to the relatively high Δt.  ASHPs using CO₂ as the refrigerant may improve things, and reduce the scope for installer set-up induced variations, but right now we at a point where if someone just gets an ASHP installed by a random installer the chances are that their SPFH2 will be lower than 3, making gas both cheaper and lower in terms of CO₂ emissions.

Actually, I think that's looking at the wrong problem, or rather installers tend not to understand the problem. Fundamentally, heat pumps are limited by the Carnot cycle - where the most critical parameter, temperature difference, is outside the control of the installer.

This is taken from published Samsung ASHP data, with a 25°C line extrapolated since the pump can run with an output temperature of 25°C but no published data is available. It appears to be pretty representative for most modern heat pumps, but probably assumes perfectly dry air. This illustrates two key points:

1. Performance - whether measured as SPF_H2, COP or anything else is critically impacted by flow temperature. There is a lot of concentration on the heat pump behaviour, but the single most critical thing is improving the insulation and fitting a system which can provide heating with a very low flow temperature (both are required together, realistically). If put in at the design stage of the sort of house most people on here are looking to build, I think 25°C flow temperatures are entirely realistic. Higher flow temperatures or poorer insulation, and the maths is rather different.
2. Even the COP at 55°C is really rather good in warmer air temperatures - and the UK is actually quite a warm place. Taking London as an example (yes, I know it has a heat island effect - but it also has an awful lot of people living there), you'd be spending 6 months of the year achieving a COP of nearly 4 on your hot water, dropping to 2 or so in December and January. The point is that the SPF value for hot water should be a lot better than the EST figures suggest, because they're mostly taken from people with big heating loads which are predominantly in cold weather - hot water use is spread out over the year, and so the average dT will be much lower than the SPF figures at 55°C would suggest.

 

[Ed Davies]

37 minutes ago, pdf27 said:

It appears to be pretty representative for most modern heat pumps, but probably assumes perfectly dry air.

So why does the COP increase going below about -5 °C? I suspect it's because of the reduction in absolute and specific humidity at those temperatures so this is not assuming perfectly dry air.

[Jeremy Harris]

@pdf27, Δt doesn't seem to be the problem, or at least not the most significant problem, the dominating factor is that ASHPs need to defrost if they are run under conditions where the evaporator can ice up.  A defrost cycle reverses the 4 way valve, so putting the heat pump into reverse, so that if it's in heating mode it will switch to cooling mode, and pump heat out of the house in order to warm up what had been working as the evaporator in order to melt any ice that may or may not have formed on it.

 

The way in which an ASHP manages defrost cycles has the most significant impact on SPF during cool, humid, weather.  Once the air temperature drops below zero the SPF actually increases for an ASHP that is being run to the point where it's been reaching the ice forming region, that combination of incoming air temperature and humidity and evaporator temperature that creates an icing risk.  It is this that means that COP is such a poor measure of real-world efficiency - one ten minute defrost cycle can lose 20 mins worth of heat energy to the house, with a commensurate loss in efficiency, which is not reflected in the COP data.

 

I found that our Carrier ASHP measures the air temperature and humidity that is being drawn in to the rear of the evaporator and uses that, together with the evaporator temperature, to determine whether a defrost cycle was needed.  It also seems to use the actual heat energy that the ASHP is delivering in that determination, as I've found, by experiment, that restricting the flow temperature to 40 deg C maximum seems to completely stop the unit from ever defrosting.  My best guess is that the heat energy being delivered with the flow set to that low a temperature isn't enough for the defrost sensing system to trigger a defrost cycle - it probably relies on the unit being able to defrost naturally as it cycles, perhaps.

 

Worst case I found was when the air temperature was around 4 deg C and the humidity was very high, a not untypical wet winter day in the UK.  My best guess is that when the compressor turns off under such conditions, there is enough sensible heat in the cool, moist air to defrost the evaporator from just the fan airflow, with no need for the 4 way valve to operate and start pumping heat out of the house.

[pdf27]

11 minutes ago, Ed Davies said:

So why does the COP increase going below about -5 °C? I suspect it's because of the reduction in absolute and specific humidity at those temperatures so this is not assuming perfectly dry air.

Good point. TBH I haven't paid too much attention to the very low temperature behaviour as that's an extremely rare occurrence in my part of the UK - worth paying attention to for system sizing considerations but not worth worrying about heat pump efficiency at. There may be other second order impacts as well (e.g. air density increasing), but you're probably right that humidity is a significant suspect.

 

2 minutes ago, JSHarris said:

@pdf27, Δt doesn't seem to be the problem, or at least not the most significant problem, the dominating factor is that ASHPs need to defrost if they are run under conditions where the evaporator can ice up.  A defrost cycle reverses the 4 way valve, so putting the heat pump into reverse, so that if it's in heating mode it will switch to cooling mode, and pump heat out of the house in order to warm up what had been working as the evaporator in order to melt any ice that may or may not have formed on it.

 

The way in which an ASHP manages defrost cycles has the most significant impact on SFP during cool, humid, weather.  Once the air temperature drops below zero the SFP actually increases for an ASHP that is being run to the point where it's been reaching the ice forming region, that combination of incoming air temperature and humidity and evaporator temperature that creates an icing risk.  It is this that means that COP is such a poor measure of real-world efficiency - one ten minute defrost cycle can lose 20 mins worth of heat energy to the house, with a commensurate loss in efficiency, which is not reflected in the COP data.

Errr... do we actually have test data to back this up? The amount of heat being applied to the ice to melt it is exactly the same amount of heat that was extracted from the water in the first place to freeze it. Additional heat will have been extracted from the dry air passing through, so all you're theoretically losing is the pumping work done to extract heat from the water to form ice in the first place.

 

At 5°C, wet saturated air contains 0.0054 kg of water per kg of air, reducing to 0.0038 kg per kg of air at 0°C - so you're extracting 0.0016 kg of water per kg of dry air cooled by 5°C.

Doing so extracts 5050 J from the air (C_p for dry air is 1010 J/kg.K) and 534 J from the ice being formed (333.55 J/g over 1.6 g), for a total of 5584 J. Assuming a COP of 3 in perfectly dry air, the heat pump will require 1861 J of electricity do to this, for a total heat supplied of 7445 J.

 

If the ice is then melted using only heat from the house the 534 J from the ice will be lost, the effective COP will be 5050/1861, or 2.71 - about a 10% hit. Annoying, but only about equivalent to increasing the water flow temperature by 2-3°C. You'll see a bigger impact on a foggy day (water content in the air is above saturation level), less so on normal days when the air is below the saturation point.

[Jeremy Harris]

Yes, I spent hours testing our unit to see how it behaved.  As it's a big name manufacturer (one that's re-badged and sold under a fair few other "brands") it seems reasonable to assume it behaves much like other units - there's only so many ways to skin this particular cat.

 

What happens (or seems to happen - remember this is test-derived, so there's guesswork as to what the ASHP is doing internally) is that when icing conditions are detected (doesn't actually have to be ice on the evaporator, either - spoofing the sensors makes it do it) the unit enters a defrost cycle.  The 4 way reversing valve operates and the ASHP runs at max power for a few minutes, drawing heat from the house (i.e the condenser becomes the evaporator and water at around 10 to 12 deg C gets sent around your UFH/buffer tank).  It stays operating like this for a time, then switches off, operates the 4 way reversing valve again and re-starts at the modulated demand required to deliver the set flow temperature (the unit power is modulated up and down in order to maintain the set flow temperature when it's switched on and in heating mode).

 

So, a ten minute defrost cycle can remove more heat from the house than ten minutes running at the normally modulated down power level. 

 

Clearly during a defrost cycle the ASHP is removing sensible heat from the house, and for several minutes after the end of the defrost cycle the ASHP is playing catch up and replacing the heat that it drew out in order to defrost, before it gets back to being a net contributor to heating the house again.  All the energy it consumes from the start of the defrost cycle to the point where it's replaced the energy lost from the house as a part of the defrost cycle is wasted, in effect, and if it's defrosting once every hour or so (not untypical if run hard in ideal icing conditions) then it may well be wasting 20 to 30% of the energy that would otherwise be used to heat the house, so lowering the SPF.

[Ed Davies]

38 minutes ago, pdf27 said:

The amount of heat being applied to the ice to melt it is exactly the same amount of heat that was extracted from the water in the first place to freeze it.

Dunno, haven't looked inside a ASHP but wouldn't a well designed one use less energy to get rid of the ice than to freeze it because not all of it needs melting. Once the bit in contact with the pipes has melted the rest should fall off still solid, shouldn't it? Or do they try to avoid that in case it finishes burying itself in its own artificial snow drift?

[ProDave]

Under certain conditions, I am surprised at just how much condensation pours off the evaperator.  I can imagine when it gets closer to 0, there is going to be a lot of cold condensate just wanting to freeze.

[Jeremy Harris]

4 minutes ago, Ed Davies said:

Dunno, haven't looked inside a ASHP but wouldn't a well designed one use less energy to get rid of the ice than to freeze it because not all of it needs melting. Once the bit in contact with the pipes has melted the rest should fall off still solid, shouldn't it? Or do they try to avoid that in case it finishes burying itself in its own artificial snow drift?

 

 

From what I can tell, they may well not be that intelligent.  Our's seems more intelligent than some, as it does at least have an external temperature and humidity sensor, that senses the air flowing into the evaporator, plus it senses the evaporator temperature (or more accurately, the refrigerant temperature flowing in/out of the evaporator).

 

If there was an easy way to detect when there actually was ice on the evaporator and then only use just enough heat to get that to start to melt and fall off, then i'm pretty sure there would be a worthwhile energy saving.  As far as I can tell it just relies on a timed cycle, though.

[pdf27]

15 minutes ago, Ed Davies said:

Dunno, haven't looked inside a ASHP but wouldn't a well designed one use less energy to get rid of the ice than to freeze it because not all of it needs melting. Once the bit in contact with the pipes has melted the rest should fall off still solid, shouldn't it? Or do they try to avoid that in case it finishes burying itself in its own artificial snow drift?

Probable, but there isn't any easy way to work out how much you would save doing this and they may not be able to spot when all the ice is gone. Easiest just to assume it's all melted with internal heat to get an estimation for power consumption.

[ProDave]

My LG unit only heats the hot water for half an hour at a time (you can set that duration) with a pause before the next round of hot water heating (another parameter you can set)  It doesn't explain why it does this.  One theory of mine is they don't want to stop space heating for too long (not that my house would even notice the heating has been off for half an hour).  But another possibility might just be a way to try and minimise icing by only doing the "hard work" in short bursts.

[Jeremy Harris]

On 27/08/2018 at 15:52, ProDave said:

My LG unit only heats the hot water for half an hour at a time (you can set that duration) with a pause before the next round of hot water heating (another parameter you can set)  It doesn't explain why it does this.  One theory of mine is they don't want to stop space heating for too long (not that my house would even notice the heating has been off for half an hour).  But another possibility might just be a way to try and minimise icing by only doing the "hard work" in short bursts.

 

I'm near-certain it's to reduce the risk of icing.  It's the high Δt that seems to cause the heat pump to work hard, and so cause the evaporator temperature to reduce to a low level, perhaps to sub-zero temperatures where it will tend to ice up.  Space heating with UFH is generally a very much less demanding requirement - in our case in space heating mode the heat pump runs at around it's lowest possible modulation level, typically around 400 to 600 W of input power. That power increases rapidly when the set flow temperature is increased, I've found.

 

My guess is that your unit may well rely on the lower heating load to act as a de-icing system for the DHW mode, by letting the evaporator warm up naturally when the load is reduced. 

 

FWIW, I've never actually seen ice on our unit's evaporator, even when I was playing around to try and see how it behaved.  It would go into a de-icing cycle before there was any visible indication of ice, just loads of condensate dripping off the evaporator.  It may well be that it does this as a pre-emptive measure, as there may possible be a risk of damage if ice does build up; there isn't much clearance between the evaporator and the rear screen.

[ProDave]

I sort of tested this short duration programing of my heat pump today.

 

Last night was a cold night here. 2 degrees I measured outside at 7:30AM  That was just the time the ASHP is programmed to start heating the hot water, which it did this morning in 2 half hour bursts.

 

It has often been said this this low temperature but above freezing is the worst conditions. Well a lot of condensation came of the evaporator, but no ice formed and it did not feel the need to do a defrost cycle.  So hopefully  that has proved in normal use defrosting should not be a regular thing.

[Stones]

I recently posted details of how our ASHP performed in my blog.  I obtained the figures from the on board metering (which seems accurate when I take into account meter readings and my daily electricity consumption).

 

In heating mode flow temperatures rarely exceed 30C and the ASHP is barely ticking over.  For DHW it does ramp up and like @ProDave and @JSHarris installations, a lot of condensate will drip off.  Ice doesn't seem to form.

[joe90]

At the risk of repeating myself from another thread on ASHP running it surprises me that on DHW mode the unit does not run till it’s about to start defrosting then simply stop. This way you could get the max DHW temp which on a good day could be 50+.rather than limiting DHW temp to worst case scenario?

Edited August 31, 2018 by joe90

[ProDave]

40 minutes ago, joe90 said:

At the risk of repeating myself from another thread on ASHP running it surprises me that on DHW mode the unit does not run till it’s about to start defrosting then simply stop. This way you could get the max DHW temp which on a good day could be 50+.rather than limiting DHW temp to worst case scenario?

That of course would be far too logical, so you can guarantee nobody will implement that.