Economy with VMC hygro

[green]

Hello,
A friend, responsible for a holiday center had a thermal assessment of her building.
Disaster balance as she suspected.
In the proposed solutions, the most profitable is the replacement of the traditional VMC by a humidity-sensitive vmc and they announce a savings of about 25% on the heating bill (gas + electricity).
For information, the heating bill is 970 000 € / year and the expected savings is 240 000 € / year.
At the sight of the numbers, I checked the characteristics of the material and it is not a vmc dual flow but a humidity sensitive.
I find the 25% savings over the 15% exaggerated by replacing all single glazed openings with double glazing or 5% by redoing the insulation of the building which must have 30 years.
The cost of the work does not enter the savings calculations.
There must be about 200 showers in the building.
What do you think ?
Goods.

[Philippe Schutt]

The most financially profitable action is often the most localized because the amount invested is lower.
Thus, vmc is usually a point of preference for a quick return on investment even if the gain is not the one you are advertising. You can test by cutting the vmc once the showers are dry.
What is the expected savings with a double-flow?
Then, if the gain with a simple humidity is to be 25%, it would mean that the buildings are already very well insulated. what surface is there? 3000 m2?

Then, the boiler and hot water production are also 2 precise investment points and therefore fast return on investment.

[dedeleco]

the 5% by redoing the insulation of the building which must have 30 years.

This gain of 5% seems to me very underestimated, because on a poorly insulated building, improving the insulation greatly decreases the thermal losses, in the ratio of the change of quality of the insulation thicknesses, for example of concrete to 10cm of good insulating, the gain is of a factor 4 to 10, neighbor of more than75%.

With 970 000 € / year, and 200 showers and how many rooms of a poorly insulated building !!
A priori 1000 rooms, 1000 € heating per room and a shower for 4 rooms ???
Otherwise with 200 rooms with one shower per room, and 5000 € heating per room, even with disastrous insulation, this expense for a single room is more than double the heating expenses of a 140 2 room 6m70 insulation old room insufficient XNUMX years !!

So these figures seem to me inconsistent.
It is necessary to know the consumption in KWh / m2 of the building, old isolated evil reaches 200KWh / m2.
It is also necessary to know the nature of the current heating, electrical, boiler of what type ???
It is also necessary to know the actual speed of the current VMC, and to quantify the associated losses.
A VMCcorrecte does not throw the heat of heating out excessively.
A humidity adjustable adjustable cheap on each shower and room can reduce these losses, when the air is dry.

It should be understood the origin of the expenses, building heating or numbers of astronomical and excessive showers, which must be limited then for example by a billed individual hot water consumption meter or individual electric meter.

Once you understand the technical origin of these expenses, it is easier to check the consistency of the thermal balance and to know if there are serious errors.
If the thermal balance does not explain in details by being able to verify each one of its precise affirmations, it is doubtful, especially for a building so important, of at least 1000 chambers ????

Normally, the double glazing is only useful after proper insulation of all the walls, because if the wall losses at m2 are comparable to those of the glazings, since the surface of the walls is very superior in general, it is well more efficient to insulate walls with 10 cm of insulation inside or outside.

So you need accurate information.

[dodo]

In the proposed solutions, the most profitable is the replacement of the traditional VMC by a humidity-sensitive vmc and they announce a savings of about 25% on the heating bill (gas + electricity).
Goods.

I do not know if it is exaggerating but on my energetic visit, the fact of changing my vmc by a vmc hygro would make me win 11% against 14 with ITE.
I also found it very bizzard.

[Philippe Schutt]

The more isolated the house is, the greater the gain in% since the divisor (total losses) is smaller, and this always for the same gain in absolute value.
knowing the flow of the vmc and the T ° of the expelled air one can calculate the energy and the cost that this represents.
there, assuming that a humidity-controlled VMC turns 2x shorter, aeration would currently expel half of the heating budget.

verdes, can you have the flow of vmc?

[dedeleco]

on my energetic visit, the fact of changing my vmc by a vmc hygro b would win 11% against 14 with ITE.
I also found it very bizzard.

This kind of statement only makes sense if the assumptions and details are explained, allowing to see the absurdities and errors.
Indeed, the degree of humidity is very variable depending on the inhabitants, between those who take 5 showers a day and those who wash once every two months!
The gains in vmc hygro will be very different.
Moreover everything depends on the flow of the starting VMC and the associated heat losses. if VMC ventilates as opening the windows in high wind, we will gain 100% by cutting it.
Same way for the ITE: 14% to gain in ITE, (a hemi) indicates that the house is already well insulated, with insulation thicknesses 1 / 0,14 = 7 times thicker than that of the ITE or almost without walls and glazing, or a big blunder in energy calculation ???
So totally agree on the weird and ask for specific explanations on the reasoning !!!