Green Building Forum - How much would secondary glazing save a shop?

How much would secondary glazing save a shop?

GarethC — Fri, 15 Sep 2023 13:16:34 +0100

Tearing my already meagre amount of hair out a bit on this one. Sure there's an easy(ish) answer.

We're trying to develop a more easily-installed form of secondary glazing specifically for outsize single glazed windows common in high street shops, cafes etc..

This kind of property should lose a greater proportion of heat through their windows, and therefore upgrading the windows should reduce heating costs and emissions by a relatively large amount.

I've engaged an energy assessor to produce an EPC for a helpful cafe that has agreed to be a guinea pig. He will produce a pre and post secondary glazing EPC rating.

He's not able to help me estimate the financial savings the cafe would realistically expect to enjoy. This particular cafe uses oil filled electric radiators exclusively, and has massive windows, so we're hoping that the figures are quite substantial.

Can anyone advise how I can go about coming up with a realistic estimate of financial savings? Can't find a calculator online....

Greatly appreciate any help. Thank you!

How much would secondary glazing save a shop?

Doubting_Thomas — Fri, 15 Sep 2023 16:47:08 +0100

The most accurate option would be to get involved in a PHPP model, but I'm assuming that may be overkill in this instance.

For your situation, there is a simpler rule of thumb involving heating degree days whereby you can work out the heat flow through the glass in its current state and then do the same calculation for 'upgraded' glazing. This assumes all else is equal in the system.

Transmission Loss = Area x U-value x Temperature Correction(fT) x Heating Degree Hours (GT)

The guide on the final page of this document takes you through the formula, but bear in mind the Gt value will be different for wherever your building is, and you'll need to find this out to get an accurate figure

https://www.markstephensarchitects.com/wp-content/uploads/2019/10/Passivhaus_Notes_2.pdf

How much would secondary glazing save a shop?

GarethC — Fri, 15 Sep 2023 18:22:37 +0100

Oh that's great thanks. In fact, if I just want to calculate a percentage reduction in heat demand, it doesn't really matter what Gt I use, does it? Then if I know the heating bill of the property, I can come up with a rough estimate of reduction in heating costs (allowing for standing charges, and presumably a comfort element). Thank you!

How much would secondary glazing save a shop?

lineweight — Mon, 18 Sep 2023 14:33:04 +0100

How will you estimate/calculate U-values pre and post secondary glazing?

I'd be interested to know what your results are and what kind of thing you develop.

I'd imagine it will be rather difficult to find a way of adding secondary glazing to shopfronts in a way that is not visually intrusive, can be easily cleaned and so on.

How much would secondary glazing save a shop?

GarethC — Mon, 18 Sep 2023 15:37:11 +0100

Well, there are glazing U-value calculators online like Pilkington Spectrum (have to register). They'll allow us to estimate the U-values pre and post pretty accurately. I was planning on engaging the Building Research Establishment to get fully modelled results, but I'm not sure if that' actually going to be necessary.

Will report back on where we end up. Certainly lots of problems to solve, but it's one of those problems that I think is desperate for a better solution.

I was in a cafe today which has outsize single glazed windows and electric only heating. It's EPR was about as low a G as you can get, and despite having had a ten year lease, other than installing LED lights the business owner had done nothing as most measures too expensive and/or disruptive.

How much would secondary glazing save a shop?

Doubting_Thomas — Mon, 18 Sep 2023 16:30:44 +0100

Posted By: GarethCIn fact, if I just want to calculate a percentage reduction in heat demand, it doesn't really matter what Gt I use, does it?

Technically I guess it's just a variable in the equation but I'd be tempted to get it at least close (mainly so you can compare against the bill), bearing in mind it won't be taking account of solar gain in the heating months so won't be a perfect fit.

There's a useful map of the regions used here:

https://www.enmanreg.org/freedd/uk-degree-day-data/

where you can also download a 20-year average in degree days. If you multiply this by 24 to get the value in degree hours (so the units work), this gives you the Gt for that region.

I just checked this on my own validated PHPP and it was pretty accurate (Gt used in PHPP was 69 for the Severn Valley region, I got 2,831 days x 24 = 67.9 from the 20 year average). Bearing in mind the PHPP works to 20Â° and the degree days assume 18.5Â°, that probably accounts for the slight difference.

How much would secondary glazing save a shop?

Osprey — Tue, 19 Sep 2023 17:01:20 +0100

Posted By: GarethCWell, there are glazing U-value calculators online like Pilkington Spectrum (have to register). They'll allow us to estimate the U-values pre and post pretty accurately. I was planning on engaging the Building Research Establishment to get fully modelled results, but I'm not sure if that' actually going to be necessary.

Will report back on where we end up. Certainly lots of problems to solve, but it's one of those problems that I think is desperate for a better solution.

I was in a cafe today which has outsize single glazed windows and electric only heating. It's EPR was about as low a G as you can get, and despite having had a ten year lease, other than installing LED lights the business owner had done nothing as most measures too expensive and/or disruptive.

It would be nice to see out without condensation-fogged windows as well, in many small cafes.

How much would secondary glazing save a shop?

GarethC — Wed, 20 Sep 2023 09:57:26 +0100

Also improved customer comfort for those sat right next to the window. Working on a discussion guide now and hope to have some genuine customer research done by the end of the month to see what business owners care about.

Lanlords in theory are expected to upgrade the EPC of their properties by law, but I've lost track of the requirements and timescales and, crucially, the get outs, of which I suspect there are many, which would allow landlords to get away with doing little or nothing... Anyone got a firm grasp on this?

How much would secondary glazing save a shop?

GarethC — Wed, 20 Sep 2023 23:40:34 +0100

Well that's my last question answered then... Not just delayed but abolished.