How do I approximate my MVHR efficency?

[Iceverge]

As per the title, I'm curious to find out the actual efficiency.

 

In use I have measured the supply temperature at 20.7deg and extract at 21.1deg. 

 

Flow rate is approx 100m3/hr. 

 

Is this enough information or do I need exhaust and intake temp too? 

 

It's a counter flow heat exchanger. I don't know the pressure drop across the unit or ducting. 

Edited October 19, 2021 by Iceverge

[A_L]

40 minutes ago, Iceverge said:

Is this enough information or do I need exhaust and intake temp too? 

 

You would need the exhaust and intake temperatures, but there are  at least two additional problems, 1) The volumes of the two flows will probably not be the exactly the same, and 2) The heat from the fan motors will be added to the airstreams.

Edited October 19, 2021 by A_L

[Iceverge]

Is it unrealistic to expect to calculate an overall efficiency in that case using only a cheapo anemometer/thermometer. 

[A_L]

2 hours ago, Iceverge said:

Is it unrealistic to expect to calculate an overall efficiency in that case using only a cheapo anemometer/thermometer. 

 

IMHO, yes. The problem will be balancing and measuring the airflow. Any condensing in the heat exchanger would be an added complication.

 

If you do not have it you may find information on your MVHR in this database

 

https://www.ncm-pcdb.org.uk/sap/pcdbsearch.jsp?pid=34

[Iceverge]

Right, that's firmly into the couldn't be arsed bin. 

 

I have the passivhaus cert and the DEAP (Irish SAP) cert but I was just curious. 

[SteamyTea]

4 hours ago, Iceverge said:

In use I have measured the supply temperature at 20.7deg and extract at 21.1deg. 

Almost there then.

https://www.engineeringtoolbox.com/heat-recovery-efficiency-d_201.html

[MJNewton]

For an approximate idea of unit operating efficiency (in terms of heat recovery - is that what you're interested in?) you can simply do (supply - intake) / (extract - intake). More accurate calculations described here.

Edited October 19, 2021 by MJNewton

[Iceverge]

Ok, I'm enthused again.  Off to do some measuring. Will report back.  

[SteamyTea]

2 minutes ago, Iceverge said:

Ok, I'm enthused again.  Off to do some measuring. Will report back.  

You can use an IR thermometer if your aim is good.

[Iceverge]

I have measured and discovered that my measuring apparatus is banjaxed. Inside temp 20 deg. Exhaust temp 20 deg. Inlet temp 20 deg. Outside temp 20 deg, in Ireland, in the night, in October. Lol.  

 

7 minutes ago, SteamyTea said:

You can use an IR thermometer if your aim is good.

 

I must make a purchase.