MVHR vs Air Con - if you had to pick one?

[Nickfromwales]

19 minutes ago, saveasteading said:

Like all those miserable people in the Mediterranean climate. It's OK.

They get it all year round. We don’t .

[Thorfun]

1 hour ago, tuftythesquirrel said:

We have a SE (18m) and a SW (22m) facing aspects and don’t need AC. If we know that it going to be 30C+ we actually keep the windows closed and use blinds to limit the solar gain. We very rarely get above 23C. So it can be done.

I like to look out at the blue sky so have AC to allow that if I wish to! We also have blinds to help with overheating but I don’t want to live in a house in permanent shade during the summer months. 

[SBMS]

I considered whether to install AC or not but have decided to fit fancoils to the first floor bedrooms and landing areas and have a two zone ASHP system. So can cool to proper AC levels in summer if needed. Wasn’t hugely more than a standard ASHP and was roughly the same as not doing UFH upstairs. And installed MVHR as well. 

[Thorfun]

17 minutes ago, SBMS said:

I considered whether to install AC or not but have decided to fit fancoils to the first floor bedrooms and landing areas and have a two zone ASHP system. So can cool to proper AC levels in summer if needed. Wasn’t hugely more than a standard ASHP and was roughly the same as not doing UFH upstairs. And installed MVHR as well. 

But can’t cool while the hot water tank is heating, right?

 

I also considered fan coils and floor cooling but it was getting complicated and seemed like a lot of faff. 
 

having separate AC and ASHP just kept it simple for me. 

[SBMS]

2 minutes ago, Thorfun said:

But can’t cool while the hot water tank is heating, right?

 

I also considered fan coils and floor cooling but it was getting complicated and seemed like a lot of faff. 
 

having separate AC and ASHP just kept it simple for me. 

True but that’s a fraction of runtime really - and can be scheduled in the early hours (when it’s cheap). Personally I think simplicity is having one system doing both, but maybe it’s my OCD not wanting a unit sitting there unused half the year. 

[Nickfromwales]

16 minutes ago, Thorfun said:

But can’t cool while the hot water tank is heating, right?

Usually PV would sort that, or just a midday blast on the immersion heater, direct from the grid, so the cooling can just plod on in the background.

[Andeh]

You can always run the pipework for AC, and first fix it.... Then in future years install the expensive bits either end. Could do it all for a few £100... 

 

MVHR is too invasive and there is no retrofitting. 

[Nestor]

3 hours ago, Nickfromwales said:

Are you cooling the GF slab with the ASHP?

I guess you intend to retro-fit the downstairs ones if you deem that necessary?

I did try cooling the slab with the ASHP but the family discipline closing windows and doors during the hot periods was iffy so gave up.

On sunny days the UVC is 67c with the immersion / PV diverter by 10am.

The lower ground floor bedrooms are north and east facing with smaller windows so not an issue.

The first floor bedrooms with vaulted ceilings are the warmest and AC is just so effective and the running cost offset by PV (+FIT).

 

 

 

 

[Thorfun]

58 minutes ago, Nickfromwales said:

Usually PV would sort that, or just a midday blast on the immersion heater, direct from the grid, so the cooling can just plod on in the background.

I didn’t install a solar diverter for our PV as I figured I’d get a better COP from the ASHP than a 1:1 using a diverter. The ASHP is also run from the PV anyway so, in theory, I believe I’m using less PV to get the tank heated. 

[Nickfromwales]

31 minutes ago, Thorfun said:

I didn’t install a solar diverter for our PV as I figured I’d get a better COP from the ASHP than a 1:1 using a diverter. The ASHP is also run from the PV anyway so, in theory, I believe I’m using less PV to get the tank heated. 

You, sir, are correct. I now routinely dissuade anyone from 'diverting' excess PV as these days it's either going into a battery or they're getting paid for the less complex method of selling and buying back. KISS at its finest.

 

Hoooooooooooooooooooooooooooooooowever....... I would like to interject.

 

In terms of promoting longevity for ones ASHP, I suggest that my clients use the ASHP at dawn, and again at dusk for recharging the DHW, and only topping up at midday off the grid, via the immersion, if it is at all necessary. I dislike the idea of having the ASHP jump from a relaxed state of cooling to a panic state of DHW recharging, and the subsequent downturn in COP.

 

I like to look holistically at how the M&E is presented at the design and concept stage, but furthermore, how long the homeowner will have a reliable system that doesn't need replacement prior to it delivering a ROI. Most ASHP's don't come with a warranty longer than 7 years, which is pretty crap, gas boilers around 10 max, so anything simple that can stave off a premature replacement of a bit of kit in the multiples of thousands, is a worthwhile pursuit imho. Kicks the beloved BUS grant saving into touch if you need to replace these any sooner than expected.