Air Tightness Test - poor result

[joth]

I also installed mvhr for comfort rather than financial payback. But it claims to have saved over 2000kWh per year since installed so will pay for itself in ten years. 

 

 

The fact it uses power is negligible. It's about 3% of the saved energy. 

 

But again, it's for the comfort. Every previous house my wife would constantly be opening windows (to remove humidity to avoid mold) and I'd be constantly closing them because it was so damn cold.  So I guess the biggest financial saving was mvhr has saved us a costly divorce 😂

 

[JohnMo]

The formula for calculating ventilation heat loss is:

Rate of heat loss = V x ACH x DeltaT x 0.33

 

So if we take the efficiency of MVHR as 85%, some better some worse.

 

The formula becomes to calculate savings 

V x ACH x DeltaT x 0.33 x 0.85.

 

So if you flow rate through MVHR as 0.3 ACH. A 200m² house with 2.4m high ceilings, inside temp 20 outside temp -3

 

(200 x 2.4) x 0.3 x 23 x 0.33 x 0.85.

 

So you are saving just over 900W against a ventilation heat loss of 1100W, without heat recovery. That is worse case.

 

So a more average winter temperature of 6 degs

 

The saving becomes an hourly savings of 600W throughout the heating season.

 

600W  x 24 hrs x 180 days. So about 2500kWh. So @joth numbers are in the correct ballpark.

 

So a CoP of 4 or gas, so around 5p per kWh. 2500 x 0.05, is about £125 a year.

 

My first quote for MVHR was £10k so that for us would have been about 80 years payback. As it is I am still looking at 16 years as DIY installation.

1 hour ago, joth said:

so will pay for itself in ten years. 

So you only paid £1000 for the full system?

[ProDave]

30 minutes ago, JohnMo said:

My first quote for MVHR was £10k so that for us would have been about 80 years payback. As it is I am still looking at 16 years as DIY installation.

1 hour ago, joth said:

I self installed mvhr for about £1500 so the payback will look a lot better.

 

But good insulation, good airtightness, 3G windows, ASHP and MVHR were the "must have's" so it was not a question of payback.

[JohnMo]

21 minutes ago, ProDave said:

But good insulation, good airtightness, 3G windows, ASHP and MVHR were the "must have's" so it was not a question of payback

True, it's a package of upgrades that go hand in hand. Good airtightness, needs forced ventilation, so why not have heat recovery as well.

 

If you aren't reasonably airtight airtight MVHR is a none starter, costing you money every minute on, payback is never, in that cases.

[joth]

2 hours ago, JohnMo said:

So you only paid £1000 for the full system?

No. However I would have paid more than 5p per additional marginal kWh of delivered heat over last 4 years, and predict I would pay more again on average over next 6 years. 

It's a weak comparison without factoring in inflation, prediction of future energy prices, and opportunity cost of tying up the capital, which ICBA to do given I didn't install for financial payback.

It's O(10) years. Good enough 

Edited Friday at 18:51 by joth

[joth]

9 hours ago, joth said:

11 hours ago, JohnMo said:

So you only paid £1000 for the full system?

No. However I would have paid more than 5p per additional marginal kWh of delivered heat over last 4 years, and predict I would pay more again on average over next 6 years

 

Actually I just realised, the 2000 kWh / year saving is compared to having perfectly managed (mechanical) ventilation without a heat exchanger. So the relevant cost saving here is the heat exchanger itself which is £800 Inc VAT (Zehnder Enthalpic) so pays for itself in under 8 years even at  5p/kWh for extra heating. (Shorter if paying more for heat)

 

In reality if I hadn't installed MVHR then we'd:

(a) have trickle vents,

(b) renovated to a much lower airtightness goal, and 

(c) have the windows open much more of the time, even in winter.

Together these three would yield far greater (and largely unmanaged) heat losses than that what the Heat exchanger is recovering. The principle savings come from the upgrade to managed rather than unmanaged ventilation, and the heat recovery is just the icing on the cake. 

 

And I should add I've also automated the window opening and closing now too, modulating the window gap according to needs in summer, so even that is managed. That's the cherry on the icing on the ventilation cake.

Edited yesterday at 04:15 by joth

[JohnMo]

4 hours ago, joth said:

Actually I just realised, the 2000 kWh / year saving is compared to having perfectly managed (mechanical) ventilation without a heat exchanger. So the relevant cost saving here is the heat exchanger itself which is £800 Inc VAT (Zehnder Enthalpic) so pays for itself in under 8 years even at  5p/kWh for extra heating. (Shorter if paying more for heat

Not something I could agree with, it's the whole cost of the MVHR system, not just a single high cost component.

 

4 hours ago, joth said:

In reality if I hadn't installed MVHR then we'd:

(a) have trickle vents,

(b) renovated to a much lower airtightness goal, and 

(c) have the windows open much more of the time, even in winter

Next logical step in ventilation would be demand based MEV or dMEV, so the trickle vents would be self actuating, and ventilation fans run at a flow rate dictated by humidity and/or CO2.

[saveasteading]

4 hours ago, joth said:

renovated to a much lower airtightness goal,

I'd say that would be wrong. Lack of airtightness is lack of control. Once you have good airtightness you can adjust and control the ventilation.....if you need to.

 

I'm very pleased that everyone who has MVHR is happy. So they should be or something is far wrong.

 

But I'm happy with everything I've done without it. None seem stuffy and  occupants have never complained. 

I think there is enough fresh air brought in to replace extracted air (kitchen/wc) or when people move around / use the door.

 

Any input on this from others? Do you have a stuffy home and wish you had mvhr?

 

15 minutes ago, JohnMo said:

dictated by humidity and/or CO2.

What a good idea. Why is that not standard? And dog or cabbage smells.

[joth]

13 minutes ago, saveasteading said:

I'd say that would be wrong. Lack of airtightness is lack of control. Once you have good airtightness you can adjust and control the ventilation.....if you need to.

Do you mean wrong morally, or you found something wrong with my logic?

We literally embarked on the deep renovation purely to install MVHR and got dragged into the whole Enerphit project as a side quest while trying to improve airtightness to fit said MVHR.

So whether it is "Wrong" or "right" I can promise you, without the goal of managed ventilation we'd have just spent a fraction of our budget doing a conventional extension and redecorate like the other 99% of house renovators "wrongly" do every year, retaining the original airtightness of a 1960s house. 

 

 

 

[Roger440]

58 minutes ago, JohnMo said:

 

Next logical step in ventilation would be demand based MEV or dMEV, so the trickle vents would be self actuating, and ventilation fans run at a flow rate dictated by humidity and/or CO2.

 

Something like this. https://glidevaleprotect.com/product/intelligent-passive-stack-ventilation-ipsv/

 

I like the concept, because it uses no power, or internet. And makes no noise. Minimal capex cost. Its just sits there doing its thing.

 

I even have an existing chimney thats redundant.

[ProDave]

I think a lot of "I am happy with my standard house, it is not stuffy" is a case of you are used to it.

 

Now we have mvhr, when I visit other houses I immediately notice the stuffy air and smells.  Particularly when visiting relatives in their 300 year old cold damp Welsh farm house.  You smell the damp as you enter the front door.  But stay there a week and you no longer notice it.  They will swear their house does not smell damp. 

[saveasteading]

26 minutes ago, joth said:

something wrong with my logic?

Apologies, I mean the logic.

For a new build or major conversion, there isnt much more work in getting great airtightness than decent. 

For extensions it has less benefit, and for refurbs it will be more difficult.

[jack]

55 minutes ago, saveasteading said:

Any input on this from others? Do you have a stuffy home and wish you had mvhr?

 

I've lived with MVHR in our new build for 9 years. I love the year-round air quality and wouldn't be without it if I ever built again. 

 

For comparison, I've lived in about 20 flats/houses over the years. The current one has far and away the most pleasant physical environment.

 

Unsurprisingly, it's particularly noticeable during cold weather. When you come in from the cold, the house feels warm but the air is still fresh. It's a qualitatively different feeling from walking into, say, a Victorian house during the peak of its evening heating cycle. 

 

All that said, MVHR isn't the only contributor to how the house environment feels. It's well insulated and uses low temperature UFH under polished concrete flooring, so it's evenly warm with no hot spots. Triple glazing means no window-driven convective drafts. 

 

Personally I think you need the combination to maximise comfort.

[S2D2]

5 hours ago, saveasteading said:

Any input on this from others? Do you have a stuffy home and wish you had mvhr?

Yes. 90s house but various improvements to airtightness, nothing drastic but better than average. PIV fitted and in combination with a dehumidifer for clothes drying solved the humidity/stuffiness issue. Something still didn't feel right, so got a CO2 meter, bedrooms can hit 3000ppm if the door is closed overnight.

 

MVHR will be going in as soon as I get round to it.