As Built SAP

[gravelld]

My understanding was that, even with a high performance fabric first design, it was really difficult to achieve "A" without renewables (which is a weakness of SAP imo). How did you manage it - do you have a heating system which ticks certain boxes? Or installed a bike rack? (only joking, I realise we're past CFSH craziness).

[Onoff]

It's not rocket science is it? Super insulated and super airtight (itself aided by the icynene spray foam insulation) and you've a near sealed box. A good proportion of any heat source is staying in there.

 

My very tentative playing around with vcls  (and penetrating them thereafter) recently has given me a whole new appreciation of "draughts" and that doing it properly pays the most massive dividends in preventing heat loss.

 

Aka the Devil's in the detail! 

Edited February 28, 2018 by Onoff

[Gone West]

12 hours ago, gravelld said:

My understanding was that, even with a high performance fabric first design, it was really difficult to achieve "A" without renewables (which is a weakness of SAP imo). How did you manage it - do you have a heating system which ticks certain boxes? Or installed a bike rack? (only joking, I realise we're past CFSH craziness).

Maybe it's an urban myth. I've always heard that said, but never seen any evidence to support it. We have a compact unit, Genvex Combi 185LS, which provides the DHW, ventilation and warm air heating.

[Mr Punter]

28 minutes ago, PeterStarck said:

Maybe it's an urban myth. I've always heard that said, but never seen any evidence to support it. We have a compact unit, Genvex Combi 185LS, which provides the DHW, ventilation and warm air heating.

 

Your own case proves it can be done.  I wonder how many points the MVHR and airtightness add?

[Jeremy Harris]

46 minutes ago, PeterStarck said:

Maybe it's an urban myth. I've always heard that said, but never seen any evidence to support it. We have a compact unit, Genvex Combi 185LS, which provides the DHW, ventilation and warm air heating.

 

I think we've discussed this before, and worked out that getting to around A94 to A96 was about as high as you could get without adding renewables, but it does depend to some extent on the shape and size of the house (big square houses are easier to get a high rating that small, long and thin ones, for example).

 

11 minutes ago, Mr Punter said:

 

Your own case proves it can be done.  I wonder how many points the MVHR and airtightness add?

 

One thing I did ages ago was to get hold of a free copy of FSAP and run through some changes like this to see how they affected the rating.  In our case airtightness and MVHR made a very significant difference. 

[Gone West]

1 minute ago, JSHarris said:

One thing I did ages ago was to get hold of a free copy of FSAP and run through some changes like this to see how they affected the rating.  In our case airtightness and MVHR made a very significant difference. 

Yes I did much the same with a free copy of, I think, SAP2005 in around 2010. It didn't help a great deal and I found using PHPP much easier. Back then they really were like chalk and cheese. I still don't understand why they don't use ACH.

[Jeremy Harris]

4 minutes ago, PeterStarck said:

Yes I did much the same with a free copy of, I think, SAP2005 in around 2010. It didn't help a great deal and I found using PHPP much easier. Back then they really were like chalk and cheese. I still don't understand why they don't use ACH.

 

 

Me too, Peter.  The disparity between SAP and PHPP is massive, and it's SAP that seems to have significant errors when dealing with houses that are very energy efficient.  PHPP gave a prediction that was pretty close to our actual house performance, SAP is just bonkers when it comes to the heating requirement!

[Guest Alphonsox]

4 hours ago, PeterStarck said:

Maybe it's an urban myth. I've always heard that said, but never seen any evidence to support it. We have a compact unit, Genvex Combi 185LS, which provides the DHW, ventilation and warm air heating.

 

We have a passive-ish spec build and are just on the border of "A" without renewables. From our current SAP calculations the next step for us would be to calculate all the thermal bridging effects and use real psi-values rather than the default of 0.15. As this costs money to do without any real world gain I'm likely to be sticking with a high "B"

[Trw144]

We re an 89A and that’s with a couple of points for solar thermal (I don’t think you get many points for solar with mains gas heating as it’s not seen as offsetting much co2). We ve got way too much glazing to get into an A rating - so I suspect it’s certainly possible to get an A rating without renewables if you are careful with your design.

Edited March 2, 2018 by Trw144