ASHP system spec

[sbm74]

Working on a tender for a c. 700m2 3 storey house; 5 bathrooms, 5 showers (2 of which run at 15 l/min); and 2 baths.  Usually occupied by 2 adults but needs capacity for 10 people. 

 

Had two quotes for the ASHP system. One has specced:

 

2x 11.2kw Ecodan AHSP 400l DHW and no buffer tank.

 

the other:

 

2x 11.2kw Nibe ASHP 800l DHW and 500l buffer tank.

 

From reading this forum and the forum about hot water cylinder sizing, I’m guessing we should be in between the two and I feel like a buffer tank is a necessity but I would be grateful for thoughts from more experienced members.

 

We’re also planning to reverse the heat pump to provide cooling in the summer and we’re getting pushback from one of the suppliers. We’re not going to be commissioning this system until after the RHI has ended.  If there are any recommendations for suppliers in the Mid Sussex / Kent region, please let me know.

 

Thanks

 

 

 

[PeterW]

What is the heating ..?? Are the ASHP just for DHW..?

 

And is 3 phase available ..? 

[SteamyTea]

Have you done a room by room heat loss calculation for the space heating (if it is doing that).

 

Seems a 500 litre buffer is rather large.

[Dan F]

36 minutes ago, sbm74 said:

We’re also planning to reverse the heat pump to provide cooling in the summer and we’re getting pushback from one of the suppliers

 

If it was me, I'd knock them off the list if they are pushing back on cooling.  I had same issue with some PV installers where they pushed back on 3-phase, I simply ruled them out.

 

[nod]

I’m just looking into ASHP

To my disappointment All three have said it’s not worth reversing for cooling 

[dpmiller]

"not worth"?

[IanR]

2 hours ago, sbm74 said:

Usually occupied by 2 adults but needs capacity for 10 people. 

 

I think you should run 2 UVC's of around 350l each, but have some control that only brings the 2nd one into to play when you need the capacity, ie. a "party" mode. It will save quite a lot of standing losses on the system when there are only 2 people in the house. You would need to include the unused cylinder in the Legionella cycle every two weeks.

 

2 hours ago, sbm74 said:

We’re also planning to reverse the heat pump to provide cooling in the summer and we’re getting pushback from one of the suppliers.

 

1 hour ago, nod said:

To my disappointment All three have said it’s not worth reversing for cooling 

 

There doesn't seem to be a lot of ASHP cooling experience with the installers. Probably due to it being disallowed on RHI up to a couple of years ago. It is "relatively" simple, as long as you pick an ASHP that can do this out the box (There's an add on for the Nibe and you need to use the SMO40 controller I believe)

But, I don't believe standard UFH controllers can handle cooling (they couldn't when I specced in 2017), and not all installers will know how to get the UFH actuators opening for cooling. (assuming you'll have multi-zones with potentially different temp requirements)

I'd assume on the build you mention you are considering some home automation. If so make sure it can control UFH actuators for cooling as well as heating and don't bother with a dedicated controller for the UFH manifolds.

 

Edited to add:

The Nibe's mentioned need 100l each of buffer (or permanently open UFH/Radiators) so a 500l buffer seems overkill

Edited August 4, 2021 by IanR

[joth]

1 hour ago, dpmiller said:

"not worth"?

Yeah adding to what @IanR said, my impression (from quotation and installation) is it's "not worth the hassle to the installer" to support cooling too. They are trying to provide competitive quotes, but doing anything "non standard" will cost them more (research time, materials, debugging/maintenance) and it's not worth the hassle. 

 

I pushed to have it supported, and issues that cropped up included:

- attempt to skimp on the main flow/return insulation before it was buried in the walls: I caught and corrected this.

- attempt to cut corner on the UFH mixing valve (using thermostatic rather than electronic actuator). I caught and corrected this.

- incomplete insulation on all the pipes/pump/valve/filters etc in plant room resulting in lots of condensation. Installer didn't even know how to insulate a pump. I invented my own solution (using sheeps wool wrap lagging)

- controller not setup right for it (but fortunately ecodan FTC6 does support it very well out of the box - I reset the DIP switch for it)

Probably some other snags I forgot now.

 

 

 

Edited August 4, 2021 by joth

[Dan F]

2 hours ago, IanR said:

I'd assume on the build you mention you are considering some home automation. If so make sure it can control UFH actuators for cooling as well as heating and don't bother with a dedicated controller for the UFH manifolds.

 

You don't necesarily need home automation for this.  If you have a limited number of zones, you can typically use ASHP wiring center to control a number of circuits, just need to check ASHP controller supports cooling.

[sbm74]

ASHP would be for DHW and space heating. One supplier has estimated a 20kW demand and the other 23kW.  Three phase power looks like it’s going to cost upwards of £50,000, which is beyond our budget, but we’re looking to get an additional single phase brought in to the property at the bargain price of £17,500.

 

I think both suppliers are being overwhelmed with new business and it’s proving extremely difficult to get any detail out of either of them. It always feels like they’re doing me a favour. Having said that, they’re both leading suppliers in this area and have been recommended to me by builders or friends who have used them. I don’t think they like it when I question their answer. “The Mitsubishi Ecodan cannot be used in cooling mode” for instance. 

 

My worry is that I don’t have the knowledge or experience that many of you have on here so I’m not going to be able to spot their errors.

 

Thanks for the advice so far. 

[joth]

1 hour ago, sbm74 said:

“The Mitsubishi Ecodan cannot be used in cooling mode” for instance. 

Yes, this is the classic response. Being generous what they mean is "The ecodan cannot be used for cooling, when installed the way we install it"

 

They have too many people asking for quotes, so they're going to take the nice simple jobs where they can be in and out in a day, no thought or return visits needed. MCS/RHI has given the whole industry a nosebleed over cooling so they just don't want to touch it.

 

1 hour ago, sbm74 said:

Three phase power looks like it’s going to cost upwards of £50,000, which is beyond our budget, but we’re looking to get an additional single phase brought in to the property at the bargain price of £17,500.

 

Another option is you could put that money into improving the levels of insulation (and airtightness) around and under the property, which will reduce the kW of ASHP needed and thus allow you to use a smaller mains supply. I would hope it will also gain dome SAP points too, which may allow some savings elsewhere. 

Finally, it will reduce ongoing annual heating bills, again saving you £ over the lifetime of the house (and/or adding value to the house)

 

Just a thought.

 

[Dan F]

1 hour ago, sbm74 said:

I don’t think they like it when I question their answer. “The Mitsubishi Ecodan cannot be used in cooling mode” for instance. 

 

My worry is that I don’t have the knowledge or experience that many of you have on here so I’m not going to be able to spot their errors.

 

There have got to me more than a couple of good installers in your area.  I'd get some more quotes until I'm confident about who I'm dealing with.  An initial phone conversation with the right person can help rule out suppliers who aren't interested in cooling etc..  We didn't use them in the end, but elite renewables, who aren't that far from you, seemed very comptetent in conversations I had with them.

[jack]

6 hours ago, sbm74 said:

One supplier has estimated a 20kW demand and the other 23kW. 

 

The house is a bit over twice the size of ours, but we comfortably get by with a 5kW ASHP. What're the insulation and airtightness targets?

[Conor]

I'm similar to Jack... 315m² over three stories, peak heading load of 5kW. Ive no idea on the style/shape of your build, build method, insulation etc... But I wouldn't hesitate to spend another £50k+ on passive House levels of insulation and airtightness. That'll get you down to a single 11kW ashp.

[Marvin]

21 hours ago, nod said:

I’m just looking into ASHP

To my disappointment All three have said it’s not worth reversing for cooling 

I'm testing how worth it is We have started to organise cooling using the ASHP. The unit can supply down to 7C. Running through the radiators at 18C we found condensation collected on some radiators. So next time we will run at 20C and see what happens.

 

Our next experiment after that will be through the coil in the MVHR

[nod]

30 minutes ago, Marvin said:

I'm testing how worth it is We have started to organise cooling using the ASHP. The unit can supply down to 7C. Running through the radiators at 18C we found condensation collected on some radiators. So next time we will run at 20C and see what happens.

 

Our next experiment after that will be through the coil in the MVHR

The three I spoke to All thought cooling effected the RHI 

It may be as already pointed out the  cooling may effect the quote 

So there trying to put customers off for that reason 

 

I and others will follow this post with interest 

[Marvin]

5 minutes ago, nod said:

The three I spoke to All thought cooling effected the RHI 

It may be as already pointed out the cooling may effect the quote 

So there trying to put customers off for that reason 

 

I and others will follow this post with interest 

Yes but I'm using it for heating. ???

[Marvin]

Advised to use port valves to separate types of emitters. So extra valve and a switch.

 

[IanR]

45 minutes ago, nod said:

The three I spoke to All thought cooling effected the RHI 

 

Up to 2017 ASHP were not permitted to cool on RHI, but that changed at the end of 2017. 

 

From the Ofgem website:

[Marvin]

Hi IanR

Thanks for this. I think you said this before. Sorry I didn't take notice. I will follow this up with my supplier..

 

M

 

[Marvin]

1 hour ago, IanR said:

Up to 2017 ASHP were not permitted to cool on RHI, but that changed at the end of 2017. 

I'm not sure what this means.

When they talk about heating a room Ofgem use the phrase "space heating". Why didn't Ofgem say "space cooling" instead of water cooling?

 

If no one knows the answer I will have to ask Ofgem.?

 

Any help out there?

[Marvin]

I am now reading the 63 pages of the ofgem Domestic Renewable Heat Incentive Essential Guide for Applicants which will be followed by 65 pages of the ofgem Domestic Renewable Heat Incentive Reference Document.

 

To try and find what is meant by water cooling....?

[Dan F]

17 minutes ago, Marvin said:

To try and find what is meant by water cooling....?

 

Simply means you have to use a air-to-water heat-pump for heating/cooling and aircon type units are not allowed.

 

[Ommm]

It is mentioned under a strange heading:

Quote

Heat pumps can’t be designed to use ‘exhaust air’:
Air source heat pumps can’t be designed to use exhaust heat. That’s residual heat which has
been expelled from a building or appliance, as in, for example, building ventilation systems.
Heat pumps that provide cooling are eligible, but RHI payments will not include energy used
for cooling. Heat pumps that only provide cooling, such as air conditioning units, are not
eligible.

https://www.ofgem.gov.uk/sites/default/files/docs/2021/03/drhi_essentialguideforinstallers_mar2021_v6.pdf

 

It's unclear if that's solely about MVHR heat pumps or applies to heat pumps generally.  If it was about MVHR the third sentence doesn't really make sense (MVHR forbidden, MVHR with cooling still forbidden, non-MVHR ASHP allowed?)

Edited August 5, 2021 by Ommm

[Dan F]

3 hours ago, Marvin said:

I'm testing how worth it is We have started to organise cooling using the ASHP. The unit can supply down to 7C. Running through the radiators at 18C we found condensation collected on some radiators. So next time we will run at 20C and see what happens.

 

If you have a humidiy sensor somewhere, and the ability to control flow temperature, you can adjust the flow temperature based on relative humidy.  Some ASHP controllers will even do this for you with requiring anything external.

 

3 hours ago, Marvin said:

Our next experiment after that will be through the coil in the MVHR

 

This will be fine at 7C, you'll just need a condensate drain for the heat battery.  Do you have your MVHR ducts insulated though?  If you don't you risk some condensation on ducts and it won't be quite as efective.  What heat battery do you have BTW?