MVHR vs ASHP enrergy comparrision if you can only afford one

[Andy Hales]

Hi,

Has anyone looked at whether it would be more efficient on a retrofit (in terms of energy use and bills) to have an MVHR with direct electric heating, or an ASHP without an MVHR?

On the particular project this question came up, I’ve modelled the house in PHPP but it’s not that low energy due to a restricted budget, so we’re trying to make the best use of the funds available. We’re maximising the insulation we can get without causing very significant cost increases e.g. not digging up the floor slab or extending existing eaves/raising the roof. I found the final energy demand and PER were significantly lower with an Air Source Heat Pump and no MVHR. Obviously this doesn’t take into account the other benefits of MVHR, but I would be interested if other people have found similar or different results.

Andy

[Gabriel Hyde]

Your result makes sense, Andy. The energy lost through the fabric far exceeds that saved by ventilation heat recovery.

I’m planning my own retrofit to the AECB Retrofit Standard. If I test MVHR vs. mechanical extract only (switching between ‘1-Balanced PH ventilation with HR’ and ‘2-Extract air unit’ on PHPP’s Ventilation tab), and assuming heat pump overall CoP of 2.5, I get the same result as you.

Even if I beef up the fabric insulation so that heating demand is reduced to 25kWh/(sq.m*a), i.e. Enerphit standard, the result is the same, though the difference is much smaller.

• This reply was modified 1 year, 3 months ago by Gabriel Hyde. Reason: superscript disappeared

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