question about HRV - ducting type?

jasperok

Considering a intervent/orcon hrc-300 MHRV unit at a cost of 2300 euros.
http://www.dealec.co.uk/acatalog/intervent_heat_recovery_systems.html

i am somewhat lost as to what specs of ducting to get though.

http://www.dealec.co.uk/acatalog/intervent_round_pipe_systems.html

there is a list of ducting made by same manafacturer as the unit.
I am torn between solid pipe or insulated ducting. both are close enough in price but is the pipe that much better than insulated flexi duct?

i considering 150mm for runs to the main extraction areas such as bathroom and kitchen and 100mm for the standard feeds.

CJhaughey

Use solid pipe. Using flexible ducting will result in a large drop in airflow due to the increased drag.
You need to draw up a diagram to work out how many elbows,T sections, and reduced size sections you will need.
You don't need 150mm going to every room in the house, 100mm will do for bedrooms.

Do-more

With any ducting system you should be trying to achieve the smoothest airflow possible.

Flexible ducting will introduce turbulance in the airflow. So smooth walled piping is far more preferable.

Also airflow does not like sharp bends so rather than using sharp 90deg bends create a large sweeping bend instead, also use Y's rather T's to manifold the various ducts into the HRV unit.

This will of course take up considerably more space than if you were to use sharp 90's and tees but if you can design it in from the begining you should help your systems efficency.

Make sure that you have some sound insulation designed into the system.
We have one section that isn't (sound) insulated correctly, Its like a voicepipe "Bathroom to Utility! do you read! over" :pac:

In reality, it isn't funny, must find a way to retrofit a sound baffle.

CJhaughey

I almost forgot, you haven't mentioned silencing, make sure that you get some silencers for the unit or you could find that the unit is too noisy to live with.

muffler

CJhaughey wrote: »

I almost forgot, you haven't mentioned silencing, make sure that you get some silencers for the unit or you could find that the unit is too noisy to live with.

My secret is out - I am indeed a silencer

muffler

muffler wrote: »

My secret is out - I am indeed a silencer

*blows raspberry through pipe!*

sinnerboy

Any system not selected from here will be reflect badly on your BER rating

http://www.sap-appendixq.org.uk/search.jsp

A default efficiency rating will be applied to the HRV and you may get a worse energy rating . Before buying ask for the

1. specific fan power is W/( l/s ) ( default is 2 - tested models on appendix Q typically 0.7 , 0.8 )
   
2. heat exchanger efficiency ( default is 66% - tested models on appendix Q typically 75, 80 , 85 % )

.

holdfast

Where are the silencers to be placed and will wrapping the pipes insulation help as you already suggested CJ. My system is currently hanging of the joists in attic space by metal hangers

jasperok

cheers lads-

geres the appendix q link:
http://www.sap-appendixq.org.uk/documents/Intervent_HRC300-4B_MVHR_BP.pdf

cant make much sense but they have it there efficiency 85% , specific fan power 0.8 W/( l/s ) specced for kitchen plus 7 wet rooms.

i'm hoping that means its a good unit.

Whats the story with these mufflers?
do they restrict flow?
surely you'll need two at the unit for unit transmitted noise and one near each valve/vent to stop noise travelling between rooms.?

AckwelFoley

You need to use insulation on the duct.
What duct did the manufacturer suggest, because normally the system is tested on the Apendix Q list with only one type of Duct.

Who calculated the pipe sizing and air volumeof the house, and how many air exchanges have you calculated it on? - be sure that this was done for the house when selecting the unit.