Alto Energy ASHP spec seems wrong?

[BotusBuild]

Seeking feedback.

I used the JHarris heat loss spreadsheet. The worst  Total daily heat loss power for mean minimum OAT that I could get was 3.246kW. That was reached by erring on the side of caution with all the input figures but being sensible about it.

I have informed Alto that the heat emitters would be UFH, and we would like a 250 or 300L hot water cylinder. I sent them the spreadsheet I had used so they had all the same input data that I had used.

 

I just got back the quote and a performance document, the latter which makes interesting reading:

1. Total Design Heat Loss - 8.53kW
2. Design Flow Temperature for Heating System - 50C
3. Design HW temp 55C with a reheat time of 1h10m

I can live with item 3 although I would likely run it a little cooler (45C), but item 1 and 2 have me baffled.

 

I have gone back to them and asked to see their detailed calculations that led them to the 8.53kW heat loss figure and I have asked why the heating system flow temp is at 50C

 

FYI - they have specified a Mitsubishi Ecodan 11kW ASHP and 250L cylinder.

 

Observations?

 

[BotusBuild]

Just got this nugget back:

However, for the size of cylinder that you require, it would need to go onto a much larger heat pump so that it has the capability of heating it.

 

Do I smell BS?

[JohnMo]

A combined, MCS heat loss spreadsheet and shite in and shite out from contractor.

 

Cylinder temp does not need to be above 50.

 

UFH will be closer to 30 to 35 I suspect.

 

If your max heat requirements are close to 3kW, you really need to look at heat pump turn down as that is a big pump. Biggest issue will be required flow rates for water. 3kW only requires around 10 l/min, you may have to manage 20+?

[MikeSharp01]

1 hour ago, BotusBuild said:

Do I smell BS?

Does have a whiff of that - ask them which university gave them their degrees in Thermodynamics perhaps. I think that all these companies have spreadsheets which don't look at the thermodynamics at all but just at demand and the double the size of the heat pump. There must be a sweet spot where the cost to them of the bigger heat pump is proportionately lower so more profitable and they can sell it you as faster reheat times.

 

However 11kW going into 200L starting at 10 deg and going to 50 deg C with 80% efficiency is 1h 3min 25.2sec so that bit is about right and if you go down to 8kW it will be 1h 27min 12.6sec. Then you are into worrying about modulation depth for great chunks of the year anyway as @JohnMo says.

[Conor]

Don't know why you'd need 11kW for a 200l tank, in reality you never fully empty a tank to ice cold and reheat to full temp. Just set hot water on 24hrs and the lower setpoint to 35c. We've never had issues with our 9kW heating our 300l tank. 

[jack]

5 hours ago, Conor said:

We've never had issues with our 9kW heating our 300l tank. 

 

Rarely any issues with a 5 kW ASHP heating a 250 L tank. I'll admit a faster reheat time would be nice a handful of times a year, but then I just hit the immersion for an hour to help speed things along.

 

If you want to keep your ASHP temperature low and your COP high when doing DHW, go for a bigger tank than you think you need.

[jfb]

I had an alto design/install which I am very happy with. 
my design had three different flow temperatures depending on the size of rads I used upstairs (Ufh down). The 50 degree figure seems very high for Ufh throughout. 
 

I know for a fact that they do over spec on the (generally correct?) assumption that insulation/air tightness design levels can underperform in real world. And they clearly want to avoid the problem of under specification that has caused many problems in the ashp market in the past. Self builds are I would think much more likely to perform as specified so you can make a case to them that their calcs can be adjusted for that. 
How many m2 is the property and what air tightness level is it ?

who was your main contact at Alto?

[sharpener]

1 hour ago, jfb said:

I had an alto design/install which I am very happy with. 
my design had three different flow temperatures depending on the size of rads I used upstairs (Ufh down). The 50 degree figure seems very high for Ufh throughout. 

 

It seems there are several different Altos out there. They have just turned down my request for rads, UFH and a TS in parallel with the HW tank, saying "I have discussed this with my technical director, and we don't have a heat pump that will permit this type of set up and unfortunately this type of bespoke design isn't something he wants to get involved in." So I am assuming that Mitsubishi don't provide the necessary control options, at least not natively.

 

Still waiting for a final Vaillant quote, which was promised as top of installers' list well before Easter.

[BotusBuild]

2 hours ago, jfb said:

How many m2 is the property and what air tightness level is it ?

who was your main contact at Alto?

260m²

Air Tightness not yet confirmed, but it will be as low as I can get it. I am sealing things as I go both inside and outside.

My contact has been Lauryn (surname retained for some privacy)

[BotusBuild]

Thank you all for your replies - I thought I might have been missing something, so I'm much happier about pushing back, but they are now saying they will need to do a room by room heat loss calculation. If that is the case I am going to treat them like I treated the window company and make them come and measure it all themselves 🙂

 

I dealt with MCS some years ago on the supplier side and didn't much like the "one approach fits all scenarios" position that was taken then and this does not seems to have been updated. There is no flexibility in the system for some of the types of houses we are building.

 

 

Edited April 9 by BotusBuild

[Omnibuswoman]

I can recommend the company we have used - Dartmoor Energy. They gave it a great deal of thought to our needs and ultimately recommended no ASHP simply because our anticipated heat demand will be too low most of the year to justify the spend (we don’t have underfloor heating), and would become inefficient trying to run a wet heating system at such a low level of heat demand. They had our budget in mind as much as their business needs. We used them for our solar panel system and we were really happy with them. 
 

[SteamyTea]

13 hours ago, BotusBuild said:

now saying they will need to do a room by room heat loss calculation

That should be standard for all heating systems as it is to do with the building, not the thermal source.

Easy enough to do your own as a double check.

 

25 minutes ago, Omnibuswoman said:

ultimately recommended no ASHP simply because our anticipated heat demand will be too low most of the year to justify the spend

Did they recommend an alternative, and what about your DHW needs?

Edited April 10 by SteamyTea

[BotusBuild]

1 hour ago, SteamyTea said:

That should be standard for all heating systems

I agree. it seems the first quote they are providing is not worth the PDF it was sent in.

 

I used to have a good room by room heat loss spreadsheet, but many PC changes over the years has resulted in its loss.

 

Does anyone have one I could plagiarize? If not, I'll look to adapt the JHarris sheet

[jfb]

I’m surprised they suggested an ashp based on what you said initially.

first thing I had to do was send over room details/insulation levels.

 

think I sent room volumes and insulation levels. You could always under size the rooms a bit or over sell the insulation if you are confident your house is being well detailed/built.

[sharpener]

24 minutes ago, BotusBuild said:

I used to have a good room by room heat loss spreadsheet, but many PC changes over the years has resulted in its loss.

 

Does anyone have one I could plagiarize? If not, I'll look to adapt the JHarris sheet

 

You might find a tool such as https://heatpunk.co.uk/home a bit easier to use as it is pre-populated with U values and radiator sizes. A bit clunky in places but it gave me similar results to several installer surveys (at least the ones I thought were plausible).

[Omnibuswoman]

6 hours ago, SteamyTea said:

Did they recommend an alternative, and what about your DHW needs

I don’t want to derail Botus’s thread, but yes. We agreed that a few 800w electric radiators plus a couple of heated towel rails would suffice, and that the solar panels would provide sufficient energy for the majority of our DHW for 8/12th of the year (as we have 9kw of panels and only two of us here). We have a My Eddi / My Harvi to divert surplus electricity from the panels to both the DHW and to the car charger.