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Poor location for ASHP, how much of an issue is it with respects to efficiency?

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(@rumballd)
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Hi all, first time poster here.

 

We have a new build house with an ASHP for heating + hot water, four zones under floor to the ground floor and rads to the 1st floor. When we moved in it was evident things were not quite right, there were no operating instructions/documentation at all and being new to ASHPs, I had an interesting time discovering how everything worked!

This was not helped by the system possibly not being fully commissioned, evidenced by silly settings to thermostats, all the zone valves being set to manual/on and the UF loop flows completly unbalanced. To top it all off there was no MCS certificate and the system wasn't registered with MCS.

Over the last year I've gradually got things straight although it took quite a while to persuade the (MCS registered) installers to issue the certification and I'm still chasing them up for warranty information.

However one issue remains and that is the positioning of the ASHP itself. It is positioned sideways in an alcove which is at the end of a blind passage with high walls all around.

ASHP

The airflow is from left to right in the picture.

The clearances to the surrounding wall just (within mm) meet the manufacturers specs but what happens in practice is the the cold outflow is funnelled round to the inlet leading to a multi degree drop in air temperature. Here is a plot of the inlet and outlet temperatures compared to power in kW for an overnight run with HW running from 3am-5am and heating for the remainder.

inlet outlet temps

 You can see that the inlet temperatures are being forced below zero resulting in multiple defrost cycles (the 'spikes' in temperature) even though ambient is well above freezing.

 

My question to you all is whether this has sufficient of an impact on efficiency/running costs to justify relocating the unit? The installers refuse to consider moving the unit as the clearances are within spec.

 

Thanks in advance for you help.

David.R.


   
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(@derek-m)
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You have already proved that the heat pump is badly sited, since the colder discharge air is being drawn into the intake. Heat pumps are designed to obtain most of their heat energy from the outside air, which if it has already been through the heat pump once, will not contain as much heat energy as a fresh air supply. Your heat pump will therefore operate less efficiently in the present situation.

Your installer obviously does not understand how heat pumps work and should be reported to MCS, who should remove the installers accreditation. Unfortunately this is unlikely to happen, since I suspect many of the staff at MCS don't fully understand how a heat pump is designed to operate.

I suspect that many of the manufacturer's specifications were taken from AC units, and may not be relevant for heat pumps.

Possibly an easy solution would be to build a framework around your heat pump, such that it draws its fresh air supply from above, and does not allow the exhausted air from being drawn back into the intake. As a test your could possibly knock something up from cardboard sheets (blue peter fashion) and monitor the result.

The alternative would be moving the heat pump to a more suitable location.

 


   
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(@bontwoody)
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A little while ago I would fully have agreed that the position of the heat pump was a problem, but have a look at this Heat Geek video before making a decision to move it

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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(@derek-m)
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Posted by: @bontwoody

A little while ago I would fully have agreed that the position of the heat pump was a problem, but have a look at this Heat Geek video before making a decision to move it

Not exactly scientific testing procedure, but quite interesting. A more scientific method would be to have two identical heat pumps, one in a cold well and the other out in the open, but of course no one will go to that extreme.

 


   
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(@bontwoody)
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@derek-m True, but I have to say I was shocked with the results 🙂

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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(@bontwoody)
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Just a thought as well that if the heat pump is moved further away to a better spot, there will be losses associated with the longer pipework too, although how large they might be I have no idea.

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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Morgan
(@morgan)
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I heard toward the end an expectation of a COP of 4 to 5.  Half that is the best I can get with a completely unimpeded site 🤣 

I think I need somebody to run the professional eye over my install this summer when the weather warms.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.


   
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(@derek-m)
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Posted by: @morgan

I heard toward the end an expectation of a COP of 4 to 5.  Half that is the best I can get with a completely unimpeded site 🤣 

I think I need somebody to run the professional eye over my install this summer when the weather warms.

One of the most important factors, along with a good level of insulation, is the heating capacity of the heat emitters. Larger heat emitters can transfer the same amount of heat energy at a lower LWT, hence the heat pump will operate more efficiently. At the heat pump end of the equation, the outside air temperature is important as far as the operation of the heat pump is concerned, but probably more important from the point of view of the heat loss of the home.

 


   
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(@derek-m)
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Posted by: @derek-m

Posted by: @bontwoody

A little while ago I would fully have agreed that the position of the heat pump was a problem, but have a look at this Heat Geek video before making a decision to move it

Not exactly scientific testing procedure, but quite interesting. A more scientific method would be to have two identical heat pumps, one in a cold well and the other out in the open, but of course no one will go to that extreme.

 

I have been trying to apply the Laws of Thermodynamics to the results obtained by HG.

Our present human knowledge indicates that 'zero' energy occurs at approximately -273C, so a few degrees change around 0C isn't going to be a great deal in the grand scheme. The temperature effect at the evaporator may be more noticeable, since the refrigerant gas would probably be in the region of -40C, so a few degrees change are a higher percentage. 

The heat pump controller probably increased the speed of the heat pump fan to make up for the loss in energy from the ambient air. Nevertheless pulling colder air through the heat pump will undoubtedly affect efficiency, particularly over the longer term. It would have been interesting to see the effect of HG's test over several days, to see if the temperature continued to fall, and have a more discernible affect.

 


   
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(@iancalderbank)
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Posted by: @rumballd

 

However one issue remains and that is the positioning of the ASHP itself. It is positioned sideways in an alcove which is at the end of a blind passage with high walls all around.

-- Attachment is not available --

The airflow is from left to right in the picture.

The clearances to the surrounding wall just (within mm) meet the manufacturers specs 

David.R.

 

are you 100% sure they are within specs? Do you have a specific link to the document that says so? the unit I'm installing for myself has a min clearance on the exhaust side of 1500mm. only the clearance on intake and sides are smaller (300mm). you really want that chilled air to dissipate, with no chance of recycling. I don't know what your unit is, but the clearance to the right side wall of the alcove (which is the exhaust, right?) just doesn't look , on a common sense basis, enough to allow the chilled air to dissipate at all.  and the fact that the space is enclosed at the other end ought to make another condition in the MI's apply (which is unlikely to be have been met, IMO).

would there be room on the existing pipework to rotate it by a few degrees so the exhaust blows more towards the opening of the alcove? if that proves positive then a pipework change to give room for more rotation might be worth asking for. The extra length needed will be trivial to no effect on efficiency. Or as derek says other obvious DIY thing would be an air baffle, to force the exhaust away, out of bits of plywood or something.

 

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs


   
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(@derek-m)
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Posted by: @rumballd

Hi all, first time poster here.

 

We have a new build house with an ASHP for heating + hot water, four zones under floor to the ground floor and rads to the 1st floor. When we moved in it was evident things were not quite right, there were no operating instructions/documentation at all and being new to ASHPs, I had an interesting time discovering how everything worked!

This was not helped by the system possibly not being fully commissioned, evidenced by silly settings to thermostats, all the zone valves being set to manual/on and the UF loop flows completly unbalanced. To top it all off there was no MCS certificate and the system wasn't registered with MCS.

Over the last year I've gradually got things straight although it took quite a while to persuade the (MCS registered) installers to issue the certification and I'm still chasing them up for warranty information.

However one issue remains and that is the positioning of the ASHP itself. It is positioned sideways in an alcove which is at the end of a blind passage with high walls all around.

ASHP

The airflow is from left to right in the picture.

The clearances to the surrounding wall just (within mm) meet the manufacturers specs but what happens in practice is the the cold outflow is funnelled round to the inlet leading to a multi degree drop in air temperature. Here is a plot of the inlet and outlet temperatures compared to power in kW for an overnight run with HW running from 3am-5am and heating for the remainder.

inlet outlet temps

 You can see that the inlet temperatures are being forced below zero resulting in multiple defrost cycles (the 'spikes' in temperature) even though ambient is well above freezing.

 

My question to you all is whether this has sufficient of an impact on efficiency/running costs to justify relocating the unit? The installers refuse to consider moving the unit as the clearances are within spec.

 

Thanks in advance for you help.

David.R.

What make and model is your heat pump?

Is there anything above your heat pump?

Is the area at the side of your home enclosed in anyway? What size are any fences?

As Ian has suggested, you should look closely at the recommended installation details, and probably try deflecting the airflow coming out, though if the area around the alcove is also enclosed, this may have limited effect.

I feel many will be interested in your findings.

 


   
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(@rumballd)
Active Member Member
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Joined: 1 year ago
Posts: 3
Topic starter  

Thank you all for your replies.

@bontwoody, the video is interesting and I noted their comments about recirculating air flow. There is a comment to the video on YouTube from Dan O'Niel where he suggests that the heat capacity of air is higher than generally realised and like @derek-m suggests above the reduction in efficiency is not as great as might be imagined.

However I would like to improve things from where they are if only to reduce the number of defrost cycles. 

@iancalderbank and @derek-m

The ASHP is a Grant Aerona HPID13R32, and the installer guide can be found here. Table 3-1 and fig 3-2 on page 11 give the minimum clearances :-

front (outflow) side > 600mm (actual clearance in my case is 602mm!)

rear (inflow) side > 300mm

LH side (front in my picture) > 100mm

RH side (rear in my picture) > 600mm (this is for access to the electrical connections)

Here is a rough sketch of the location. (apologies for the crude drawing)

plan view

Note that there is nothing above the alcove and we jam the solid wood gate open in Winter to encourage a flow of air down the passage. This gate is going to be replaced by an open metal structure gate in the near future.

Interestingly, when we visited the site a few months before completion the unit was rotated 90 degrees from its current orientation. However, I suspect that it was impossible to get access to the electrical panel this way around. 

old orientation

 

My plan of action is to first try a quick 'n dirty barrier from the internal corner of the alcove to the ASHP and then to see if it is practical (£) to rotate the unit by about 30 degrees clockwise to allow the outflow to be directed towards the (open) gate.

 

If anyone is interested I'll post the results here.

 

 

 

 

 


   
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