MVHR DiY install?

[dpmiller]

I hope you have more success on the BMS side than some of the lab suites I've been in. Inputs vs feedback vs actual stable control is one heck of a black art...

[Jeremy Harris]

16 minutes ago, dpmiller said:

I hope you have more success on the BMS side than some of the lab suites I've been in. Inputs vs feedback vs actual stable control is one heck of a black art...

 

 

Same here.  Even with multiple air lock doors to subdivide lab ventilated areas it was still a challenge to get the BMS to control airflow rates.  Someone closes a fume cabinet door and the pressure drops in the extract system, causing flow rates everywhere else to change.

 

My inclination would be to never try and use any form of moving air valve anywhere in the system, except, perhaps, for heat exchanger bypass.  Balancing a system is hard enough with fixed flow valves/restrictors, especially if it's anything other than a dead still day outside.  The slightest wind causes pretty wide fluctuations in airflow, something that I hadn't appreciated until the first time I tried to balance our system.  I had to give up and wait for a still day to do it, and I know that, even though our system is balanced when there's no wind, the slightest breeze throws the airflow rates out by 50% or more.

[dpmiller]

Yup. Spent too long fitting extra relays to Microflows to signal fan on, back in the day. And that was when they had the Mk1 auto speed control which used a resistor/thermistor pair for feedback & isolation. SLOOOWWW response...

[joth]

Very interesting (and quietly reassuring) to hear.

 

My current design keeps MVHR and a/c ducting completely separate. MVHR will be installed and balanced out as normal. The bedrooms each get a second, linear, air inlet grille ducted from the recirculating fan coil which can do hot or cold air to those rooms only. (Downstairs has ufh). While the doubling up of ducting into each room feels inelegant, it's the simplest way I can see to ensure the rarely used a/c cannot comprise performance of the constantly used MVHR.

The fan coil will work in an all-or-nothing mode initially, but if we find some rooms badly overheat while others are still calling for heat, it looks fairly easy to retrofit electronic dampers at the manifold. AliExpress has some bargains for this. Even then it just becomes all of nothing binary control on a per room basis, no attempt to dynamically balance the airflows as it's completely independent of the MVHR. 

As a well insulated house so I don't expect to need this per room control, but the one scenario I can see it being useful if aging guests want their bedroom much warmer than we do, it'd be useful to let them set a higher temp than the rest of the house. This might force the rest of the house heating to deactivate completely, but as the fan coil is coming from the ASHP so I'd not loose much effeceiency even if that does happen. (But knowing I can retrofit dampers is reassuring, basically the equivalent of retrofitting TRVs to radiators)

 

 

 

[gc100]

On 31/08/2019 at 10:59, joth said:

Very interesting (and quietly reassuring) to hear.

 

My current design keeps MVHR and a/c ducting completely separate. MVHR will be installed and balanced out as normal. The bedrooms each get a second, linear, air inlet grille ducted from the recirculating fan coil which can do hot or cold air to those rooms only. (Downstairs has ufh). While the doubling up of ducting into each room feels inelegant, it's the simplest way I can see to ensure the rarely used a/c cannot comprise performance of the constantly used MVHR.

The fan coil will work in an all-or-nothing mode initially, but if we find some rooms badly overheat while others are still calling for heat, it looks fairly easy to retrofit electronic dampers at the manifold. AliExpress has some bargains for this. Even then it just becomes all of nothing binary control on a per room basis, no attempt to dynamically balance the airflows as it's completely independent of the MVHR. 

As a well insulated house so I don't expect to need this per room control, but the one scenario I can see it being useful if aging guests want their bedroom much warmer than we do, it'd be useful to let them set a higher temp than the rest of the house. This might force the rest of the house heating to deactivate completely, but as the fan coil is coming from the ASHP so I'd not loose much effeceiency even if that does happen. (But knowing I can retrofit dampers is reassuring, basically the equivalent of retrofitting TRVs to radiators)

 

 

 

 

Hi @joth, what A/C system did you go with?

 

Thanks

 

[ProDave]

@joth have you sourced your fan coil units yet? if so which ones and from where?

[joth]

42 minutes ago, ProDave said:

@joth have you sourced your fan coil units yet? if so which ones and from where?

Spec is for a Carrier 42NH 235 or equivalent, but still waiting on quotes so supplier and price TBD. 

 

10 hours ago, gc100 said:

 

Hi @joth, what A/C system did you go with?

 

Thanks

 

 

Single fan coil in the loft driven from the same ASHP as downstairs ufh, air ducted into each room and recirculating back via the hallway. Went for this largely on the suggestions on here, and as we didn't want radiators in each room, which would have had to be huge or fan assisted to work with the ASHP and I reckon won't be used very often anyway.