Positive-Input ventilation (PIV) in heat-loss calculations

[Garald]

[one more chapter in the heat-renovation saga...]

 

I'm doing heat-loss calculations now to determine what heat-pump to get. The spreadsheet I am using asks me, naturally, whether I have MVHR or a ventilation system without MVHR.

The answer is really neither, since I am getting a positive-input ventilation system, hooked up to the heat-pump:

 

https://www.ventilairsec.co.uk/products/hydro-r/

vmi-technologies.com/wp-content/uploads/2020/09/aquarea-purevent-visionR.pdf   (sorry, in French)

 

But what should I enter in the spreadsheet then? Or should the rule of thumb be that I'll obtain a heat loss somewhere between MVHR and no MVHR? Where in between, more or less?

 

(The spreadsheet is giving me a total heat loss of 5.2kWh with MVHR and 6.2kWh without MVHR.)

 

 

[ProDave]

You have a ventilation system without mvhr.  The only difference between what you have and just trickle ventilators, is you know the ventilation rate, trickle vents it is a guess and depends how windy it is.

 

Are you units right there?  Do you mean 5.2kW Vs 6.2kW  i.e. you need 1kW less heating if you fitted MVHR?

[JohnMo]

PIV is a ventilation system, you are just blowing in, instead of sucking out.

 

Assume ventilation rate is based on humidity CO2 etc?

 

You may want to get humidity based trickle vents also, so if the humidity is below 50% the trickle vents close themselves and open as the humidity rises.

 

I would use something like 0.3 ACH. 

 

[Garald]

5 hours ago, ProDave said:

You have a ventilation system without mvhr.  The only difference between what you have and just trickle ventilators, is you know the ventilation rate, trickle vents it is a guess and depends how windy it is.

 

Sure. At the same time, preheating the air (or cooling it in the summer) by means of water from the heat-pump (that's what the Hydro'R/Aquarea system is) allegedly does give energy savings over just using radiators, or so the manufacturer says.

 

5 hours ago, ProDave said:

 

Are you units right there?  Do you mean 5.2kW Vs 6.2kW  i.e. you need 1kW less heating if you fitted MVHR?

Right, 1kW/hour less.

[JohnMo]

If the heat pump is heating the air the ventilation efficiency at heat recovery is zero.  You are not recovering any heat from the outgoing air.

 

The heat added by the heat pump is being generated and used by the house the same as another radiator would.  Efficiency improvement may be there but will not be massive.  Assuming an ACH of 0.3 air transfer can deliver about 10W/m2 (if I am remembering correctly), without the air smelling of burnt dust.  

 

[Garald]

4 hours ago, JohnMo said:

Assume ventilation rate is based on humidity CO2 etc?

That's what it says: "Blown air flow rate varied according to indoor and outdoor humidity".

 

4 hours ago, JohnMo said:

 

You may want to get humidity based trickle vents also, so if the humidity is below 50% the trickle vents close themselves and open as the humidity rises.

I can ask, though, as I said, the system adjusts itself based on humidity.

 

4 hours ago, JohnMo said:

 

I would use something like 0.3 ACH. 

 

 

0.35 is the lowest setting.

[Garald]

1 minute ago, JohnMo said:

If the heat pump is heating the air the ventilation efficiency at heat recovery is zero.  You are not recovering any heat from the outgoing air.

 

Correct.

 

1 minute ago, JohnMo said:

The heat added by the heat pump is being generated and used by the house the same as another radiator would.  Efficiency improvement may be there but will not be massive.  Assuming an ACH of 0.3 air transfer can deliver about 10W/m2 (if I am remembering correctly), without the air smelling of burnt dust.  

 

 

That would be about 1.5kW in my case, but the improvement would obviously not be that, but a certain percentage of that, representing the efficiency gain (how much, I do not know; what would be a sensible rough guess?). Would it be higher at a higher ACH? I did the heat-loss calculation with ACH=0.6, if I remember correctly.

[Garald]

Conversely: how much cooling can 0.6 air transfer deliver? The one and only way in which I plan to use my heat-pump for cooling is to cool the air being sucked into the building (by the same device that heats it in winter).