Heat recovery performance

[LinearPancakes]

Finally got the MVHR system on yesterday after a lot of work and time.

 

It's a Zehnder Q350 in a cold loft with terminals on the roof and Zehnder manifolds for supply/extract. Ductwork is Lindab steel with varying amounts of armaflex vapourtight insulation in the loft and on supply in the house (also have ComfoPost).

 

Now I still have more insulating and balancing to do, but the heat recovery performance is not what I was expecting. On low (160 m3/h), seeing 21.6 degrees extract, 14.7 outdoor and 16.1 supply.

 

The condensate drain is connected, I've ran the commission programme, covered the whole unit in mineral wood (to test), bypass is disabled. The unit seems be auto balancing the extract and supply flow rates anyway, though I did try covering supply terminals to make sure it wasn't over supplying.

 

Any ideas?

[JohnMo]

Have you balanced the the supply and extract nozzles room to room. If you haven't it's shite in shite out, not commissioned.

 

Unless set up correctly what your screen says is meaningless.

[MikeGrahamT21]

I think even uncommissioned that seems way out.

 

you’ve not got a pipe connected up wrong somewhere have you? Double check everything.

[Conor]

You got your ducts connected up correctly? I.e. you're not just pulling exhaust air back in?

[jack]

If you swap the supply and exhaust temps it looks about right:

 

Extract 21.6

Exhaust 16.0

Outdoor 14.7

Supply 20.3

 

Is it possible the temperature sensor leads have been plugged into the wrong sockets on the control board, or have otherwise been swapped?

[LinearPancakes]

Many thanks for the responses guys.

 

For sure the system is not balanced room-to-room. But the overall air resistance across supply vs extract is pretty balanced, and the machine appears to be adjusting the fan speed to match the flow rates anyway. My understanding is that overall extract/supply flow rates need to be matched to get optimal heat exchange performance.

 

I double checked the connections and pretty sure they're right. It's a right hand unit, so external on the left, internal on right right like the attached picture.

 

I called Zehnder support. He mentioned they once had a case of the bypass actuators failing. I took the front panel off and indeed the bypass actuators aren't doing anything on change - except a brief buzzing noise. From the pictures I could find, it looks like they're both stuck in bypass mode. Hence the limited heat recovery.

 

I'll be in touch with Paul Heat Recovery (supplier) or Zehnder on Monday. Hopefully it can be repaired in place!