ASHP for heating setup

[swisscheese]

Hi All,

 

I'm sure this has been done before and in depth, but as a kind of straw poll what do people find the most efficient configuration of providing heat to the home.

 

As we have just having our first coldish spell using the ASHP.

 

I'm thinking about:

Temperature Compensation vs A Set water discharge Temp.

Thermostat timers vs No timers.

Constant Thermostat temperature, or a couple of degree differentials.

 

Anything else?

 

 

 

 

[ProDave]

We went for keep it Simple.  Fixed flow temperature to UFH no weather compensation. Just controlled with standard room thermostats in each room connected to standard manifold controller.  All working well so far. 

 

Controlled by a conventional central heating programmer, on all day from 6AM to 9PM off at night because I want a silent house at night (still have a noisy pump issue to sort out)

 

Been down to almost -10 so far and house remains warm and energy use is exactly in line with modelled prediction.

[Jeremy Harris]

We do much the same as @ProDave, run the ASHP at a constant temperature and just use a normal room thermostat for control.  Seems to work perfectly, with the house staying within about half a degree inside no matter what happens outside (and it was sub-zero again last night here).

[ragg987]

I use the compensation control that is already built into the heat pump, so no extra stuff required other than the separate controller / thermostat. Though it took a but of fiddling to find the best heat curve, the ones pre-programmed were not suitable for our build.

 

The flow varies from about 22C to 30C when below zero outside.

 

I found leaving it on all the time to provide the best COP, when I use the timer it took a big hit. Presumably this is as it runs at a higher temperature differential due to cooler slab.

[ProDave]

I was at a house today where coincidentaly they were having the ASHP serviced.  The owner was asking about the heat curves etc and the installer was talking them through it.  They were running a heat curve that put the UFH water at 40 degrees when it was 0 outside !!!! and if I heard it right, up to 45 by the time it got to -10

[Jeremy Harris]

49 minutes ago, ProDave said:

I was at a house today where coincidentaly they were having the ASHP serviced.  The owner was asking about the heat curves etc and the installer was talking them through it.  They were running a heat curve that put the UFH water at 40 degrees when it was 0 outside !!!! and if I heard it right, up to 45 by the time it got to -10

 

IIRC, that's not that dissimilar to the default curve that ours came with, except I have a feeling that it went to even higher temperatures under those conditions, which inevitably resulted in it doing lots of defrost cycles.  I've not seen ours defrost at all now I have it set to a constant 40 deg C; it seems that our system never puts enough load on the unit for it to reach the defrost threshold.  Having a unit with probably three or four times the output we actually need for heating probably helps, as it means the evaporator is over-sized for our needs.  This means that the fan and compressor tend to run at about their lowest speed most of the time.  Heating isn't our biggest electrical demand, either, most days it's less than the hot water demand.  What I need to do is systematically work through the low power, always on, loads, as they seem to be some of our biggest energy consumers.    It's things like the ~1 kWh/day to run the treatment plant and the ~ 0.8 kWh/day for the water UV treatment unit, that push our background load up.

[swisscheese]

 

1 hour ago, ragg987 said:

I use the compensation control that is already built into the heat pump, so no extra stuff required other than the separate controller / thermostat. Though it took a but of fiddling to find the best heat curve, the ones pre-programmed were not suitable for our build.

 

The flow varies from about 22C to 30C when below zero outside. 

 

I found leaving it on all the time to provide the best COP, when I use the timer it took a big hit. Presumably this is as it runs at a higher temperature differential due to cooler slab.

 

9 minutes ago, JSHarris said:

 

IIRC, that's not that dissimilar to the default curve that ours came with, except I have a feeling that it went to even higher temperatures under those conditions, which inevitably resulted in it doing lots of defrost cycles.  I've not seen ours defrost at all now I have it set to a constant 40 deg C; it seems that our system never puts enough load on the unit for it to reach the defrost threshold.  Having a unit with probably three or four times the output we actually need for heating probably helps, as it means the evaporator is over-sized for our needs.  This means that the fan and compressor tend to run at about their lowest speed most of the time.  Heating isn't our biggest electrical demand, either, most days it's less than the hot water demand.  What I need to do is systematically work through the low power, always on, loads, as they seem to be some of our biggest energy consumers.    It's things like the ~1 kWh/day to run the treatment plant and the ~ 0.8 kWh/day for the water UV treatment unit, that push our background load up.

 

I'm currently set on a compensation curve - but the unit is defrosting more frequently than I would like,  and then working hard to reach temp when the thermostat timers knock the temp down overnight, possibly too much.

 

So it may have the wrong compensation curve, or be slightly undersized ASHP for the temperature, I did all the calcs as did others and the 9Kw unit should be enough.

 

I think I'll try a KISS methodology and set a flow temp and limit the temperature differentials on timers on the thermostats and see how it goes.

 

[ProDave]

A few of us have found if you limit the flow temperature to 40 degrees that seems to mostly eliminate defrosting.  So set a fixed temp or adjust the heat curve so it never goes over 40.

 

In cold weather it may just be better to leave it on all day and night with no set back.

[ragg987]

45 minutes ago, swisscheese said:

working hard to reach temp when the thermostat timers knock the temp down overnight, possibly too much

I think this is what gives the poor COP, hence I leave it on all time at the same temperature. FYI, here is the custom curve I arrived at by trial-and-error, seems to work well for our low energy build.

 

And an image of an optional setting that means I can be hands-off all year round and the HP takes care of itself.

[ragg987]

Should point out - that Auto On/Off setting is based on a 24hr average.

[swisscheese]

Thanks chaps, @ragg987 @ProDave @JSHarris

 

I went for the simple fixed temp solution first off.  A little tweak on some of the UFH flow rates also seems to have evened things out. So far Energy consumption has reduced. I'll play along for a bit. I might return to weather compensation once I get to grips with the Samsung unit and their explanation of the Water Law.

[Fonyt]

Hi folks, I know this post is really old, but I'm at a loss and it's the only one that I could find on Google that is relevant to some issues I'm having.

 

Our heat pump has been running constantly recently and it's costing us a fortune, about 6 months ago the machine was knocked off during a power outage and was reset to factory, I followed the recommended setup but it's not been right since. Our thermostat is set to 21°c, but room temp at 22.5°c (way too warm - verified with a separate temp gauge).

 

The company who installed our Yutaki M Heat Pump have since gone out of business and any of the literature I've found I can't really make sense of.

 

Could anyone explain the the points, gradient and fixed modes for me, what do the temperature relate to? Any recommendations for a generic setup for the UK climate.

 

Thanks in advance.
 

[MikeSharp01]

Hi - And welcome to the forum, I am sure someone who knows more than I will be along shortly.

 

Power outages can do damage to stuff as well as resetting it so it may be that you stat is damaged, if you wind the stat right down does the ASHP stop working? At any rate probably best to provide some details of the setup. Does it also do Domestic Hot Water (DHW) or just heating? Do you have a schematic of your system you can share with us?

[J1mbo]

Fixed flow temp is the worst possible configuration for ASHP. This is why the controls have sometimes almost endless configurations all centred on reducing the flow temps whenever possible.

 

That said, if it’s an underfloor heating setup needing only 30* flow anyway, then clearly all that complication is going to yield minimal gain.

Edited January 15, 2022 by J1mbo

[Fonyt]

58 minutes ago, MikeSharp01 said:

Hi - And welcome to the forum, I am sure someone who knows more than I will be along shortly.

 

Power outages can do damage to stuff as well as resetting it so it may be that you stat is damaged, if you wind the stat right down does the ASHP stop working? At any rate probably best to provide some details of the setup. Does it also do Domestic Hot Water (DHW) or just heating? Do you have a schematic of your system you can share with us?

 

1 minute ago, J1mbo said:

Fixed flow temp is the worst possible configuration for ASHP. This is why the controls have sometimes almost endless configurations all centred on reducing the flow temps whenever possible.

Thanks for your replies.

I don't have a schematic, but I can provide an overview of our system.

• House is 230m2 with 4 thermostat controller bedrooms
• Hitachi Yutaki M4 11 kW Monobloc Heat Pump & Hitachi Main Controller
• Air permeability 1.4 m3/h.m2
• Underfloor heating throughout
• Hot water cylinder
• 1 circuit covering downstairs and upstairs
• Downstairs wireless thermostat controls the overall system - so in theory when it hits its temperature (21°c) it turns the both the circuits off.
• Upstairs thermostats are wired and only control the manifolds, they are set to close at 18°c.

The system is currently set on points and looks like this:
 

Let me know if there's any other information that would help, thanks.

[Kevm]

I have radiators with my ASHP and that curve is hotter than mine.  Should it be lower?

[J1mbo]

It should be set so that the desired temperature is just reached and maintained. The idea is to have the lowest water temperature possible.

[Kevm]

I know, my compensation curve is fine, I was just thought that 37-45C was hot for a ufh system considering my rads aren't even that hot.

[J1mbo]

ah gotcha, yes it seems so but then again 11kW for 230m2 also seems like a lot unless perhaps there is a lot of hot water demand.

[joth]

1 hour ago, J1mbo said:

ah gotcha, yes it seems so but then again 11kW for 230m2 also seems like a lot unless perhaps there is a lot of hot water demand.

It depends on the heat demand and the emitter size, neither of which were given. The larger the volume in the UFH loops, the lower temperature they can run at for the same power delivery. There is one clue though:

> Upstairs thermostats are wired and only control the manifolds, they are set to close at 18°c.

This reduces the system volume, thereby increasing the flow temperature required to achieve the needed power delivery. This may result in a less efficient (more expensive) system than if you let all the rooms stats call for heat together. (i.e., remove the room by room zoning)

 

Given the overall system is driving the house to too high a temperature, that suggests:

a) that flow curve is too high. I'd try reducing it to 30-40 deg C range and experiment from there. 

b) there's whole-house room stat is not working, so it's in a permanent call-for-heat state. How much of an issue that is depends on how hard it proves to get the compensation curve dialled in.

 

Presumably you don't have any delicate wood floors or the like? These generally don't want to be above 26 deg C, which IME means keeping flow temps below 35. (I use a temp probe in the screed to back off the max allowed flow temp as the screed warms up)

 

[Fonyt]

On 18/01/2022 at 10:30, joth said:

It depends on the heat demand and the emitter size, neither of which were given. The larger the volume in the UFH loops, the lower temperature they can run at for the same power delivery. There is one clue though:

> Upstairs thermostats are wired and only control the manifolds, they are set to close at 18°c.

This reduces the system volume, thereby increasing the flow temperature required to achieve the needed power delivery. This may result in a less efficient (more expensive) system than if you let all the rooms stats call for heat together. (i.e., remove the room by room zoning)

 

Given the overall system is driving the house to too high a temperature, that suggests:

a) that flow curve is too high. I'd try reducing it to 30-40 deg C range and experiment from there. 

b) there's whole-house room stat is not working, so it's in a permanent call-for-heat state. How much of an issue that is depends on how hard it proves to get the compensation curve dialled in.

 

Presumably you don't have any delicate wood floors or the like? These generally don't want to be above 26 deg C, which IME means keeping flow temps below 35. (I use a temp probe in the screed to back off the max allowed flow temp as the screed warms up)

 

Sorry, I completely forgot about my post here, seems notifications weren't enabled. Thanks for the reply.

 

I'm still sort of seeing this same issue a year later, I have reduced the curve and it's now set to 28°c at low ambient temps and 20°c at high ambient temperatures, but it still keeps running even after it hits 21°c though it doesn't go as high as 22°c now, maybe this is how it's meant to operate? Is it by design that it runs constantly to maintain temperature? I just assumed it would turn off as soon as it hits 21°c.

 

Some other measures I've taken: I've since checked online and tried rebinding the wireless stat and on the controller it is showing the temperature that is set on the wireless stat (I changed it to lower and higher temps to make sure it was updating and not showing 21°c as a default), so it doesn't seem to be a faulty stat.

 

There is something I happened upon by accident, when I manually turn the pump off at the controller (after it hits 21°c) and turn it back on again, the pump stays off - obviously this is not a practical solution.

[joth]

@Fonyt do you have a buffer tank?

It could be the controller is configured to expect one but there isn't one. So it keeps the pump running trying to get a non existent buffer up to setpoint+5° or something like that, that it will never achieve 

[PhilT]

10 hours ago, Fonyt said:

it still keeps running even after it hits 21°c though it doesn't go as high as 22°c now, maybe this is how it's meant to operate? Is it by design that it runs constantly to maintain temperature? I just assumed it would turn off as soon as it hits 21°c.

Mine cycles between the set temp and one degree above which is fine for me. The manufacturer has confirmed that's the way it's designed to operate otherwise it would keep switching on and off around the set temp. I have radiators

Edited January 13, 2023 by PhilT

[Fonyt]

1 hour ago, joth said:

@Fonyt do you have a buffer tank?

It could be the controller is configured to expect one but there isn't one. So it keeps the pump running trying to get a non existent buffer up to setpoint+5° or something like that, that it will never achieve 

No buffer tank installed.

[joth]

2 hours ago, Fonyt said:

No buffer tank installed.

Have you confirmed the controller is not setup to think there is one, ever since the factory reset last year? This was an issue on my install at one point.