Demand Controlled Ventillation

murphaph

We're looking to install the following system from -snip- as part of our new build:

-snip-

Anyone tried anything like this?

893bet

For a new build? Forget it.

You might aswell install a MVHR system. This will cost more of course (not sure of figures but I would guess twice as much) but will be worth it.

I do like the DCV systems but ultimately HRV is far superior. Futhermore, MVHR may well be a requirement for you to meet Part L depending on the house design etc.

BryanF

DCV for reteofits
MVHR for new

Effects

Are the benefits that good from MVHR over DCV? My architect has advised against MHRV.

murphaph

893bet wrote: »

For a new build? Forget it.

You might aswell install a MVHR system. This will cost more of course (not sure of figures but I would guess twice as much) but will be worth it.

I do like the DCV systems but ultimately HRV is far superior. Futhermore, MVHR may well be a requirement for you to meet Part L depending on the house design etc.

Part L doesn't apply as we're building in Germany. There are of course similar regs here but the house will require 70% of the energy of a house that complies to the German equivalent of "Part L" before we install any form of ventilation system (very well insulated, triple glazing and highly airtight, independently blower door certified) so we don't "need" to install anything to achieve a notional efficiency.

Getting lower (down to the next step of 55%) does not benefit us financially in any way as the incentive is in the form of a lower than normal interest rate 50k loan, but our mortgage is through a family member and it is already cheaper than the subsidised rate, so anything we install will be for comfort more than anything.

The quote for MHRV was indeed (much) more than twice as much for DCV. The energy assessor for the house builder (house builder offers both systems and don't care either way what we choose-there's no pressure from them to even have any system at all) suggests that the DCV they offer is approximately 80% as efficient as a full on MHRV and reckons the difference in cost would never be recuperated in our lifetimes. he says they achieve this "close enough" level of efficiency by using patented fibre strips that tense up when the air is relatively moist (indicating poor air quality) and pull the inlet open and then slacken off when the air becomes less moist and so partially close the inlet.

It may be that the cost of these systems is much higher here due to the fire regs: The air from these systems, MHRV or DCV must be vented at roof level and the ductwork has to be enclosed in a fire resistant shaft to stop fire spreading between floors through the ventilation system (I think this requirement is overkill as fire can just as easily (much more easily in fact) go up the stairs, but the regs are the regs and the fireproofing the ducting obviously has a huge cost implication for a system with double the ductwork (MHRV).

I wanted full on MHRV as well but the wife is not at all enthusiastic about the costs and so the DCV option came into play as I really don't want to be opening windows to ventilate.

How do MHRV systems typically react to room occupancy? I mean, I want there to be more fresh air coming into the bedroom when I'm in bed and less when I'm downstairs in the living room and vice versa. Do MHRV systems also typically have inlets that adjust according to current air quality? I looked at one system here and they seem to offer an electronic CO2 sensor that can manipulate the slits in the inlets, but that is an optional extra.

Calahonda52

Whats the estimated annual running costs for the MHRV system and whats the meter cubed airflow requirement?

Intuitively I don't like the DCV's but that is just a personal "bias"

murphaph

I don't have figures for either, but I found an interesting study comparing DCV and MVHR systems and it appears things are really not as clear cut as might be thought.

Link to pdf

In the conclusion:

Demand control can bring a standard MEV system to a similar level
as MVHR when considering IAQ, CO2 exhaust, primary energy
consumption and energy costs. Besides, due to the automatic
detection of the IAQ in the different rooms, the guarantee on good
IAQ is higher when compared with a manually-operated
mechanical system without sensors. The total cost or net present
value of qualitative MEV systems with or without demand control
is nearly half that of a qualitative MVHR system, due to the higher
investment and maintenance cost of the latter.

hugo habicht

Even better if you have a demand controlled MVHR

Calahonda52

hugo habicht wrote: »

Even better if you have a demand controlled MVHR

Will this pass muster with the Irish Building Regs?

hugo habicht

Calahonda52 wrote: »

Will this pass muster with the Irish Building Regs?

What Irish Building Regulation are you referring to?

BryanF

hugo habicht wrote: »

Even better if you have a demand controlled MVHR

Can we presume your taking the piss? Before a host of posters go looking for this?

murphaph

If building regs were of no concern, would posters agree that a DCV system that is say 80% as efficient as an MVHR system but costs half the price should be considered, given the initial cost of MVHR and the ongoing cost of filter replacement?

hugo habicht

BryanF wrote: »

Can we presume your taking the piss? Before a host of posters go looking for this?

No, I am not. But no point looking for it, as far as I know you can't buy this (the op asked that question). But I am installing that at the moment. Since there is no point venting rooms with nobody in it I calculated electricity savings of around 60% compared to an ordinary heat recovery venting system (more if you do not have an open plan house design). The air flow to empty rooms is reduced to a minimum using flaps in the pipes and the fan speed reduced accordingly.

Wrt 80% as efficient: that depends on the overall insulation properties of the house. In my case venting losses are siginificant, so for a new building I would also advise a MVHR system.

bcoll05

Hello.
Just wondering did the original poster go with DCV over MHVR?
If so what's it like?

Jakey Rolling

Have been looking at making my MHRV "demand controlled" in that I want to tie in humidity and CO2 sensors to automatically boost flow rate when required. This already exists as an expensive add-on for my Brink system, but there a number of dirt cheap wifi capable sensors and relays available now that could be piggy-backed on top of the mechanical switches that we have in place.

I should even be able to tie it in to my SmartHome network, via IFTTT webservice, so you can say "Alexa, boost fan for 15 minutes" before taking a shower. *That's* demand controlled ventilation!

KCross

Jakey Rolling wrote: »

Have been looking at making my MHRV "demand controlled" in that I want to tie in humidity and CO2 sensors to automatically boost flow rate when required. This already exists as an expensive add-on for my Brink system, but there a number of dirt cheap wifi capable sensors and relays available now that could be piggy-backed on top of the mechanical switches that we have in place.

I have this in my Brink HRV system.

I have wireless buttons in the kitchen and near bathroom where you can change the fan speed or just do a max boost where it will automatically return to normal levels after 15mins. We use this regular enough.

There is also a humidity sensor in the duct and that can also causes it to boost automatically. The humidity has never been an issue so it doesn't boost for that reason so it seems that the humidity sensor was a waste of effort.
e.g. After showers the normal extraction from the system has the steam cleared within a few minutes.