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Posted (edited)

I've had my as designed SAP report done and I'm wondering whether it's worth querying the figures or whether it doesn't matter in the slightest.

 

The house isn't designed to PHPP but is an energy efficient build with passive slab; it has lots of glazing.  The as designed score is coming in at 84.

 

From what I can see, the chap doesn't understand that I have a pcm thermal store; in fact, he has assumed no thermal store whatsoever as I told him that I wouldn't have a hot water cylinder and sent him info on the sunamp instead.  From looking at the figures, it assumes that all heating is electric (correct) and when not powered by PV, will be at a standard electricity day time tariff.

 

The figures also appear to include a whole host of thermal bridges, including sills, lintels and the intermediate floor.

 

Am I making a fuss about nothing?

Edited by vivienz

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As long as its good enough to look like its going to pass when it gets to the 'as built' stage it honestly does not actually matter too much unless you are motivated to get a good result.

 

I am not familiar with current full SAP software but it is likely that he has ignored the Sunamp as there probably is no way to enter such a new system in the software. How has he actually entered your DHW?

 

The thermal bridges will be conservative default values which will hopefully significantly over estimate the energy use or they are 'approved details' with already defined values.

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He has no thermal store at all and DHW is entered as 'independent' and instantaneous at point of use.

 

Unless I'm reading the report wrongly, I don't think it has passed at this stage as it says in the header block to the report that it has failed the general compliance requirements.

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I would ask Sunamp for a solution as they are bound to have had this problem already. Instantaneous DHW would give a better result than reality as there would be no allowance for storage and distribution loss. What fuel is used for the instantaneous DHW? What are the TER and DER values?

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I wouldn't worry about the design SAP too much, but personally I'd enter the Sunamp PV as a 150 litre thermal store with an immersion and a heat loss rate of 0.6 kWh/24 hours, at this stage, as it's not that critical.  The PV section should account for the generation from renewables side.

 

Sooner or later Sunamp are going to have to come up with a way to get these things to have an appropriate means of including them within SAP, which doesn't look to be that easy to me.  We did our SAP assessment when we still had a thermal store fitted, so didn't have to jump this hurdle, but in essence all I did when swapping the thermal store for the Sunamp was change the units over, so the main difference to the rating would have been the much reduced heat loss rate.

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Okay, thanks both.  I shall worry about more important things for the time being and deal with this at the end of the build.

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1 hour ago, vivienz said:

Okay, thanks both.  I shall worry about more important things for the time being and deal with this at the end of the build.

 

Please don't. A fail at the 'as built' stage could be costly and inconvenient to correct.

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So, as the guy has said that it has failed general compliance requirements, does that actually mean what it implies and do I need to get the figures re-done to accurately reflect the situation?

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2 hours ago, A_L said:

I would ask Sunamp for a solution as they are bound to have had this problem already. Instantaneous DHW would give a better result than reality as there would be no allowance for storage and distribution loss. What fuel is used for the instantaneous DHW? What are the TER and DER values?

 

Perhaps @AndyT can comment on how they've helped customers with as built and built SAP ratings. With their new units there will be an increasing number who have them as their only and primary storage medium.

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1 hour ago, A_L said:

 

Please don't. A fail at the 'as built' stage could be costly and inconvenient to correct.

Is the design figure not deemed as provisional only?

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I've got the same problem - I have a pair of Sunamps and should be submitting a "As Built" SAP in the next few months. From playing with SAP2009 I can see that whether a hot water store is described as a Thermal Store or a plain cylinder makes no difference to SAP. The SAP HW calculation is primarily sensitive to the water volume and the manufacturers declared loss factor.

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1 hour ago, Alphonsox said:

I've got the same problem - I have a pair of Sunamps and should be submitting a "As Built" SAP in the next few months. From playing with SAP2009 I can see that whether a hot water store is described as a Thermal Store or a plain cylinder makes no difference to SAP. The SAP HW calculation is primarily sensitive to the water volume and the manufacturers declared loss factor.

 

Spot on.  All you need to do is decide on an equivalent volume thermal store.  I believe that Sunamp suggest around 120 litres, which I think is a bit pessimistic, based on experience, which is why I suggested 150 litres.  In practice, the combination of 70 litres of buffer preheat plus a single first generation Sunamp PV outperforms our old 210 litre thermal store.

 

Sunamp have already done the heat loss tests, hence the 0.6 kWh/24 hours I gave earlier.  Whether this has changed with newer units I'm not sure, but this low loss rate will make a significant difference to the DHW heating requirement in SAP, I'm sure.

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Posted (edited)

@vivienz have you discussed this with your SAP assessor? Could be that he is treating the sunamp correctly within SAP. An all electric house will prove difficult to get a pass, due to the high CO2 emissions, unless PV used. Perhaps someone from sunamp ( @AndyT ) will be along soon to advise. Also all linear thermal bridges should be noted and assessed so this listing should be there and is important.

Edited by Nickfromwales

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On 4/10/2018 at 14:28, Barney12 said:

 

Perhaps @AndyT can comment on how they've helped customers with as built and built SAP ratings. With their new units there will be an increasing number who have them as their only and primary storage medium.

 

I would be happy to try and help - please pm me.

Kind regards

AndyT

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On 4/10/2018 at 20:37, ADLIan said:

@vivienz have you discussed this with your SAP assessor? Could be that he is treating the sunamp correctly within SAP. An all electric house will prove difficult to get a pass, due to the high CO2 emissions, unless PV used. Perhaps someone from sunamp ( @AndyT ) will be along soon to advise. Also all linear thermal bridges should be noted and assessed so this listing should be there and is important.

 

Do please PM me to discuss.

Kind regards

AndyT.

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would a public discussion on this not be more useful?

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Got to agree. More useful if public to be any use for the OP. Noticed this was discussed on here a couple of years ago with no real resolution.

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Bringing this back to the top in the absence of further information.

 

The original assessor is correct, the Sunamp adds nothing to the electric heating and it is treated as an instantaneous space & water heater, no thermal store is accounted for.

 

The fact that the house is all electric will account for the relatively low EPC rating even if very well insulated, the PV helping the rating though.

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Unfortunately, I haven't had a reply to my PM to @AndyT. I have had a reply from the SAP assessor this morning, though, and he has added in a 90l hot water tank linked into the PV. This has made the difference of +2 points on the score but, more importantly, graded as acceptable in the overall design. I will post detailed comments later but it's a bit tricky at the moment as my internet connection is down for a couple of days.

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