Setting hrv airflows

comerboy

Hi everyone. First thread excuse me for lack of info but feel free to ask if need more.I've installed my hrv system in my new build and are now moved in a year and half. The system was never balanced properly but doesn't seem to be to far off can't really fault it yet. I would like to pick ye re brain to find out does anyone know how to balance the system or what instruments il need. Thanks in advance.

threeball

comerboy wrote: »

Hi everyone. First thread excuse me for lack of info but feel free to ask if need more.I've installed my hrv system in my new build and are now moved in a year and half. The system was never balanced properly but doesn't seem to be to far off can't really fault it yet. I would like to pick ye re brain to find out does anyone know how to balance the system or what instruments il need. Thanks in advance.

You'll need a vane anemometer. It should have a cowl to cover the outlet/inlet and record the airflow, normally in m3. You'll need to calculate how much airflow should be required in each room and adjust the vents to suit. Whoever you bought the system off should be providing you with the info if it was design and supply.
http://www.testolimited.com/testo-417-vane-anemometer

comerboy

I don't think I got any of that info so I'm on my own as regards that design aspect. How would I go about working out air flow, air changes etc. Would there be a cheaper alternative to those test equipment. Would easiest option to get someone to commission it for me. Is there anyone in South east that does that work.

touchdown77

I'm also interested in having someone calibrating/commissioning my HRV (with the proper equipment), any suggestions?

Borzoi

touchdown77 wrote: »

I'm also interested in having someone calibrating/commissioning my HRV (with the proper equipment), any suggestions?

To get a proper commissioning engineer to lookat a domestic hrv system would probably cost you €400 plus for a half days work. If you can hire an anemometer you should be able to give it a bash. The CIBSE guidelines for ventilation are 10-12 liters per second per person of fresh air. I can't remember the extract rates for bathrooms of the top of my head

comerboy

I thought to get the proper flow rate it was a calculation of size of room number of people etc. Setting vents would not be the difficult part would like to know for sure flows first. I also presume the system needs to be balanced i.e the total intake into house needs to equal extract.

Borzoi

comerboy wrote: »

I thought to get the proper flow rate it was a calculation of size of room number of people etc. I also presume the system needs to be balanced i.e the total intake into house needs to equal extract.

In general the supply and extract flow rates will be equal that's the way the HRV units are. When sizing up the unit you've extract from bathrooms, utility and maybe kitchen, on the supply side you've bedrooms and living spaces.

There's 2 methods of calculating airflow volume required. For supply air is best to work on the litres per second per person, for extract its number of air changes per hour.

TBH you can fudge the figures quite a bit.

touchdown77

Is it better to have the supply fan running faster (say 10% faster) than the extract fan?

The thinking being that there is positive pressure within the house.

CJhaughey

touchdown77 wrote: »

Is it better to have the supply fan running faster (say 10% faster) than the extract fan?

The thinking being that there is positive pressure within the house.

I'd run the extract more than the supply, the last thing you want to do is push wet air into the house fabric, you want to extract it.

comerboy

So next question how many litres per person is needed fresh air and how to calculate required extract. I presume all depends on size of room. I guessing I should have been giving this info with unit yes/no?

Outkast_IRE

comerboy wrote: »

So next question how many litres per person is needed fresh air and how to calculate required extract. I presume all depends on size of room. I guessing I should have been giving this info with unit yes/no?

No you wouldnt be given it with the unit, the person who specified that unit should of carried out the calculation and then picked a suitable unit that would meet the desired air flow rate. If this calculation was not done first day then the unit may be oversized or undersized.

If oversized it would be increased electrical costs and decreased efficiency, if undersized you will never achieve the desired air flow rates in each room.

Follow this to get you started .

Step 1. Calculate the desired volumetric flow rate of air in each room, this can be done either on Air changes per hour or Litres per person per second. (This may Help http://www.engineeringtoolbox.com/air-change-rate-room-d_867.html) but you will want a volumetric flow rate m3/s or m3/h . Cibse generally reccomend around 10Litres/person/second

Step 2. Check if you unit can meet or exceed that volumetric flow rate.

Step 3. Get your vane anemomneter and go around and check what each room is and how it compares to your calculations

touchdown77

CJhaughey wrote: »

I'd run the extract more than the supply, the last thing you want to do is push wet air into the house fabric, you want to extract it.

Well that would help my situation because my bathrooms are very slow to clear of steam after a shower, after an hour the tiled walls still has condensation on them and it feels steamy.

When you say the last thing you want is wet air pushed in, do you mean outside air? its that not de-humidified by a certain amount by going through the heat exchanger?

Anyhow, I plan to reverse my settings to supply at 50% and extract at 60% and see what the effects are.

CJhaughey

touchdown77 wrote: »

When you say the last thing you want is wet air pushed in, do you mean outside air? its that not de-humidified by a certain amount by going through the heat exchanger?

Anyhow, I plan to reverse my settings to supply at 50% and extract at 60% and see what the effects are.

I mean for example in your bathroom, the last thing you want with a pressurised house is the moist air in the bathroom or kitchen being forced into the house fabric.
HRV in my experience results in a very dry house if used correctly.

comerboy

Thanks outlast_ irl. When setting vents then when have all flows required what sequence. ie close all vents start at first? Does fan need to be at full speed?

Outkast_IRE

comerboy wrote: »

Thanks outlast_ irl. When setting vents then when have all flows required what sequence. ie close all vents start at first? Does fan need to be at full speed?

Energy efficiency would dictate that the lowest speed you can run the fan yet still meet all desired air flow rates is your goal.

Sequence is usually close all vents and then start at the furthest away vent from the fan and work your back to the closest vent to the fan. At the end you will need to go back to the furthest vent and check and adjust if necessary