Efficiency level of MVHR?

[Ferdinand]

Can anyone quote me a specific example or two of the efficiency level of an MVHR system, and supporting data?

 

I'm having a debate elsewhere (about how far we can reduce energy demand in narrow boats, of all things), "90%" has been quoted for MHVR efficiency (I had quoted 75%-80% for HR extract fans), and someone has asked for evidence for the 90% 🙂.

 

Thanks

 

Ferdinand

[Chanmenie]

Have a look on the websites for MVHR manufacturers 

try Vent Axia or Zehnder  or BPC 

https://www.bpcventilation.com/

[JohnMo]

You have to careful when you compare, it's actually on an apples with apples basis. As there are several ways to calculate efficiency, for example passivhaus institute use a different method to most.

 

The energy required to raise one cubic metre of air through one kelvin is 0.33 watt-hours, i.e. its heat capacity per cubic metre is 0.33 Wh m–3 K−1. Thus the total ventilation heat loss, Qv , will be:

 

Qv = 0.33 × n × V × ΔT watts

 

So using a 100m3, and a change rate via mechanical ventilation of 0.3, -3 outside and 20 inside

 

0.33 x 0.3 x 100 x 23 = 228W heat loss 

 

Same calc for 90% eff

0.33 x 0.3  x 100 x (1-0.9) x 23 = 23W heat loss

 

Same calc for 80% eff

 

0.33 x 0.3  x 100 x (1-0.8) x 23 = 45W heat loss

 

So we are taking quite small numbers an additional 0.5kWh a day at worst (when comparing 80 to 90%) in a boat that possibly leaks heat like seize anyway.

 

If your boat isn't air tight and leaks enough to ventilate itself, without additional mechanical ventilation, then MVHR actually adds to the heat losses, as its ventilation is over and above normal air leakage.

[SteamyTea]

Boats have high humidity inside them, and most of the time outside of them.

So the enthrapy calculations don't count for much.

The biggest problem with a narrowboat, thermally, is the dreadful surface area to volume ratio.

And that 0.3m of it is underwater. And what is above water is in the wind.

 

But the upside is that a small Water to Water Heat Pump could get a very high CoP.

Side and roof mounted PV will also reduce over heating if you can dump the excess energy somewhere.

 

One of the Birmingham Universities had a solar powered narrowboat as a project a decade ago.

A bit of googling seems to only show their latest hydrogen project.

Hydrogen is hopium.