Big money on eco upgrades for a 8 point DROP on SAP

[miike]

My design SAP used a lot of standard assumed data, such as double glazed windows, no MVHR, gas boiler, numerous openings for air extraction etc. It had a score of 87 B. 

 

The actual build used significantly more insulation, 3G windows, MVHR, ASHP. The costs of the upgrades would be in the tens of £ks. After submitting all this info, my energy performance was downgraded to a C with an 8 point drop to 79. 

 

I thought the assessor must be entering something wrong so I got access to a trial version of SAP assessment program and re-did the info myself. Nope, it somehow actually gave me an even lower score of 73. I removed the MVHR and added vents, changed the ASHP to a mains gas boiler and straight back to 87. 

 

I understand how these can drop a SAP score because it focuses on electricity costs and these are electric devices, but it was interesting to see that none of the other improvements moved the needle by a single point. 

 

Out of curiosity, I started playing with some of the data and gave it an air tightness score of just above 0 and boosted the u-values of all the materials - I managed to get 1 additional point. 

 

The only thing that made any real difference was adding PV and a battery, which took it from between 93 to 100, depending on the kWh inputted. 

 

The lesson seems to be, if you want an A rating, is to keep everything standard, no 'eco' heating or ventilation systems, minimum insulation for building regs, and then just add a bit of PV. Might be useful for anyone needing to qualify for an Ecology mortgage. 

[Kelvin]

Which SAP version is that based on?
 

A114 here (SAP 2012 V9.92)  I have all the things you say not to add. However, I also have an 8.45kWp PV array and batteries (not sure if the batteries make a significant difference) If I spent between £15k-£25k I could get that up to A125. No thanks. My understanding is that SAP 10 favours more ‘eco’ friendly houses. 
 

eta just checked the as designed SAP score which was B92. I can’t see that this included a PV array though as that section of the report is blank. 

Edited August 8 by Kelvin

[Gone West]

2 hours ago, miike said:

The lesson seems to be, if you want an A rating, is to keep everything standard, no 'eco' heating or ventilation systems, minimum insulation for building regs, and then just add a bit of PV.

I'm not sure that is correct. My PH house had a SAP rating of A95 without any renewables and that was in 2017 using SAP 2012 V9.92. This was achieved by having very low U values for the fabric of the building and good airtightness.

[JohnMo]

I started as designed with a B87 (from memory) that was double glazed, MVHR target airtight of 3 and a gas boiler, stove, 3kW of PV

 

Completed, still had a gas boiler, stove same PV, improved airtightness added 3G windows and more insulation, but most importantly got all the standard details corrected for actual. Jumped to A93.

 

With the ASHP have taken all the d credits for how it will be controlled?

[nod]

The final sap really means nothing As it relies on you being truthful If buyers where bothered over a sap rating Builders would simply say they had upgraded everything 

Our U values for windows where taken from estimates supplied They had no way of knowing if I had installed these Or put the bare minimum of installation 

I questioned why MVRH would lower my sap rating and was told that opening a window was far more economic 

 

   Sap is a outdated box ticking exercise at best and needs to be scrapped 

[Kelvin]

It is indeed open to abuse but I did have to provide some evidence to the assessor that at least some of what I was claiming I had actually done. Agreed though literally no one will ever ask me for the EPC other than it has one at selling time because it has to. 

[miike]

This is all done on the latest SAP 10 standards. I've attached some screenshots showing the score change from making one alteration to the spec, leaving all else the same. I reset the spec to the original before changing a new data field. 

 

I start on 87 B with no ASHP or MVHR, 0.15 u for roof and 0.1 u for walls. 

 

Air Tightness - no change in score between 6.60 and 0.10

Roof u-value (251m2 gross area) - 1 point change between 0.35 u value and 0.05

Adding MVHR - 5 point reduction to 82

Adding 6kW PV + 12 kWh battery - increase of 8 points to 95

 

Changes to data but keeping the PV and battery in the spec:

 

Main heating source changed from mains gas to ASHP - 12 point reduction to 83

Flat roof u-value - improving u-value from 0.15 to 0.1 has no effect. Worsening the u-value to 0.7 drops the score by 3 points to 92

 

 

[-rick-]

Have you completed the details fully to come up with the number or just the basics? I don't know the app but I note that the heatpump efficiency is marked at 100% in your screenshot. In reality a good install should be 400-500%.

 

You need the detail to be correct to get good output. I've seen many on hear saying they initally got bad numbers but once all the little details were added it came out better. SAP is still a flawed system however.

[Mike]

8 hours ago, miike said:

I thought the assessor must be entering something wrong so I got access to a trial version of SAP assessment program and re-did the info myself. Nope, it somehow actually gave me an even lower score of 73. I removed the MVHR and added vents, changed the ASHP to a mains gas boiler and straight back to 87. 

I'm out of touch with the latest changes to SAP, but last I heard there was going to be an (option/requirement?) to test the MVHR installation and award the score based on that -a potentially significant improvement. Sounds like that didn't happen?

 

I know that MVHR was scored low because it was based on seriously out-of-date assumptions that didn't reflect current best practice. Though with a test some installations were so poor they would be expected to score less, not more.

[miike]

6 hours ago, -rick- said:

Have you completed the details fully to come up with the number or just the basics? I don't know the app but I note that the heatpump efficiency is marked at 100% in your screenshot. In reality a good install should be 400-500%.

 

You need the detail to be correct to get good output. I've seen many on hear saying they initally got bad numbers but once all the little details were added it came out better. SAP is still a flawed system however.

Yes, took ages copying all the details into the new one before making changes. That 100% isn't for efficiency, it's for percentage of heat i.e. how much of the heating for the house is done by that unit (for situations where you have multiple sources). 

[MikeSharp01]

16 hours ago, miike said:

got access to a trial version of SAP assessment program and re-did the info myself

Which version did you use?

[miike]

4 hours ago, MikeSharp01 said:

Which version did you use?

 

SAP 10.2, it's the latest version used for all post 2022 builds. 

[MikeSharp01]

2 minutes ago, miike said:

SAP 10.2, it's the latest version used for all post 2022 builds. 

yes - sorry, I meant what brand of trial version did you use.

[miike]

52 minutes ago, MikeSharp01 said:

yes - sorry, I meant what brand of trial version did you use.

 

Elmhurst Energy, there's a 14 day free trial here but the actual license fee isn't too bad. I think they took over Stroma, which was who I'd seen recommended here previously. 

 

Edited Saturday at 11:35 by miike

[miike]

23 hours ago, Kelvin said:

Which SAP version is that based on?
 

A114 here (SAP 2012 V9.92)  I have all the things you say not to add. However, I also have an 8.45kWp PV array and batteries (not sure if the batteries make a significant difference) If I spent between £15k-£25k I could get that up to A125. No thanks. My understanding is that SAP 10 favours more ‘eco’ friendly houses. 
 

eta just checked the as designed SAP score which was B92. I can’t see that this included a PV array though as that section of the report is blank. 

 

I spent some time putting together the differences battery size makes when paired with different PV systems. It varies quite a lot on the PV kWp and also whether or not you have an ASHP. 

 

Figures used for PV/Battery costs are from here

 

1. This shows the gain from PV with no battery and no ASHP

 

 

2. PV, no battery, with ASHP

 

 

3. Battery sizes (5, 10 and 15 kW) paired with different PV kWp. No ASHP

 

 

4. Battery sizes (5, 10 and 15 kW) paired with different PV kWp. With ASHP

 

 

5. Ranked by cheapest cost (total cost of PV + Battery) per SAP point gained. No ASHP

 

 

6. Ranked by cheapest cost (total cost of PV + Battery) per SAP point gained. With ASHP

 

 

 

[Kelvin]

Has SAP10 been recalibrated like the energy rating for electrical items has been? 
 

Incidentally based on those costs my install wasn’t too bad. £15400 (before grant)  for 8.45kWp, 24kWh battery storage, gateway, bird mesh and G99 application. 

Edited Saturday at 14:01 by Kelvin

[Bramco]

Would be interesting to see the last charts by Battery kW, then cost per SAP point.  In terms of our thinking, 5kW of battery wasn't going to achieve a lot but then deciding whether to go 10 or 15 was.   Same goes, I guess, for PV. The costs of installing 2kWp would be crazy and that shows I think in the earlier sheets.

[SteamyTea]

@miike

Nice to see the software reports the battery power, rather than the energy stored.

 

[JohnMo]

2 hours ago, Bramco said:

costs of installing 2kWp would be crazy

Not really I just installed an additional 1kWp was about £400, for everything, doing 2kWp would add £200.