Posted by: @sttpd1917

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. I watched the HG video on flow temperature, but that didn't answer my question (or I didn't understand it....)  Can someone tell me why HG doesn't give this number?

No, they should, ask the question!

@jamespa Thanks, will do.

@sttpd1917, @jamespa has cut straight to the heart of it! They should provide this, and I would ask for it in writing before taking the proposal any further.

The design flow temperature is not a minor technical detail. It is one of the central numbers around which the whole proposal is built. It determines the output available from every radiator, influences the heat pump’s capacity at the coldest design condition and has a direct bearing on the predicted efficiency and running cost.

Without it, you cannot properly compare the three proposals. A radiator schedule that looks perfectly adequate at 40C may be marginal at 45C and entirely different again at 50C. Equally, the nominal size printed on a heat pump tells you very little unless you know the outdoor temperature and water temperature at which it is expected to meet your home’s heat loss.

The same applies to any predicted SCOP. That figure is only meaningful when you know the operating assumptions behind it, and design flow temperature is one of the most important.

This omission is particularly odd because Heat Geek’s own explanation of its design process says homeowners should be shown the choice between higher and lower flow temperatures and how those options affect upfront cost and long-term savings. Is this a ZeroDisrupt proposal by any chance?

If it is, the temperature may well have been calculated within the design software but simply not shown in the proposal. ZeroDisrupt is supposed to identify the leanest design capable of meeting a chosen efficiency target, while showing the customer the trade-offs. If that is what has been used here, the resulting design temperature should be disclosed rather than remaining hidden inside the process. 

I would ask them to confirm the design flow temperature at your local outdoor design temperature, the room-by-room radiator outputs at that temperature, the chosen heat pump’s output at that actual duty point, the proposed weather-compensation settings and the basis of the predicted seasonal performance.

I'll just caveat that by saying that this does not necessarily mean the Heat Geek design is poor. It may simply be inadequate documentation. But documentation is part of the design, especially when a homeowner is being asked to compare competing proposals and commit a significant amount of money.

@editor Thank you for the detailed response. I’ll report back once I’ve got a reply from HG.

Posted by: @sttpd1917

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@editor @jamespa Thank you for the detailed response. I’ll report back once I’ve got a reply from HG.

HG responded quickly. Proposed flow temperature 43. This is in line with one of the proposals and lower than the other one.

Thanks again for your assistance.

@sttpd1917 nice one. Have you received the proposal via the HG platform/website or installer direct?

@editor I went through HG website, so should be ok for HG guarantee. If I‘m brave enough to go for it 😬 

I was told that installer doesn’t get to see the system design temperature until commissioning is complete. I can live with that given the minimum guaranteed SCOP. My minimum SCOP is 4 and earlier this year my system was happily chugging along at a heating curve level of 0.2.

i had a very cursory inspection by MCS today. It took the guy 10 minutes. He checked that the HP was level and he took photos of the controls and RCBs. I got no feedback other than he now wished that he used HG for his installation.

Posted by: @l8again

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I was told that installer doesn’t get to see the system design temperature until commissioning is complete. I can live with that given the minimum guaranteed SCOP. My minimum SCOP is 4 and earlier this year my system was happily chugging along at a heating curve level of 0.2.

That was similar with us (on the design temperature), we noticed that there was no design temperature shown in the earlier documentation. We are happy with our guaranteed SCOP (including hot water) of 3.75. 
The commissioning survey did show a design temperature. But to be honest, since not all the rad upgrades were registered (we had our own plumber doing some of them), I expect that it was over estimated. 
But reading the posts here, i am being picky. The whole process was pretty smooth, plenty of post commissioning docs with photos etc.  Given how much care our Heat Geek took to install original Vaillant wall brackets (suitable for external insulation - a very elegant finish), I doubt MCS could find any gap anywhere. HG handle all the overheads very efficiently.. 

Of course our pump has only done hot water and cooling so far.. 

I have looked through the documentation again and the only reference to heating temperature that I can find is the flow temperature at which the system was tested at during commissioning:

I recall that when the system was installed, the heating curve was left at 0.9. We awoke the following day to a very hot house (min.temperature overnight was +2C) and we lowered the heating curve down to 0.2 over a series of days. I suspect that when Winter next comes the final setting might be slightly higher. FWiW, Valliant documentation states the following

• Curve of 0.4: Gives a design flow temperature of roughly 35°C (Ideal for high-efficiency underfloor heating).[1]
• Curve of 0.5 to 0.6: Gives a design flow temperature of roughly 38°C to 40°C (The gold standard Heat Geek target for ultra-efficient radiators). [1]
• Curve of 0.7 to 0.8: Gives a design flow temperature of roughly 42°C to 45°C (Standard efficient radiator setup). [1, 2]
• Curve of 1.0 or higher: Gives a design flow temperature of 50°C+ (Likely means your system is running like a traditional boiler and losing efficiency)

Posted by: @l8again

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I recall that when the system was installed, the heating curve was left at 0.9. We awoke the following day to a very hot house (min.temperature overnight was +2C) and we lowered the heating curve down to 0.2 over a series of days.

@sttpd1917 @l8again 

When we had it commissioned the decision was to leave it at an optimistic 0.5.

The plan is, when the weather cools, we will adjust the lower end of the curve manually and then when it gets really cold use that to adjust the overall curve..

Hg will come back then to adjust the rads etc but I suspect we will do most of it ourselves.