Calculate your instantaneous heating power requirement from the DPE

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Calculate your instantaneous heating power requirement from the DPE

by FabricePaille » 28/11/21, 11:22


The DPE offers to know the approximate evaluation of the energy consumption of a building. But with a very simple calculation also offers to know the need for power at the low limit temperature, to determine the impact of work. Important values ​​for sizing heat emitters.

1) Recovery of annual heating consumption:

In your DPE, in the final energy consumption column, retrieve the heating value A in kW.h / year

For example A = 4928 kW.h / year

2) Collect your DJU:

Go to website
Select the weather station for your department.
Click the arrow to the right.
Take the "energy professional" and "heating" calculation with a temperature of 18 ° C
Select the date from 1/10/19 to 31/05/2020 (the figures are only public 6 months later, but we can consider that the winters are similar).
Accept the terms of use and start the simulation.
Add up the totals (you should have a number between 1000 and 3000): B
B is your unified Degrees day by year with the unit ° C / day.year

For example B = 1800 ° C / day.year

3) Calculate the energy requirement C:

C = (A / B) x1000 / 24
C is your energy requirement in w / ° C. That is to say that this figure expresses your need for power with respect to the difference between your interior temperature and exterior temperature.

For example C = (4928/1800) x (1000/24) = 114 w / ° C

4) Determine the lower limit temperature:

Note the altitude of your house, marked on page 5 of the DPE
Go to the map: ... otherm.jpg
Using this map and your altitude, determine D, your lower limit temperature in ° C.

5) Calculate your power requirement Pmax

The maximum power corresponds to the maximum loss, therefore to the power requirement of your frame at the coldest time of the year. This data is crucial since it is the minimum power to install so that your home does not drop in temperature.
Pmax (w) = C x (18-D)

For example: Pmax (w) = 114x (18- (-10)) = 114 x 28 = 3192 w

6) calculate your overall U.

The global U corresponds to the overall conductivity of your frame. Its interest with the DPE is to compare each U of wall with your overall U. In this way, it would be advisable as a priority to work the high U which are your main centers of loss.
The first thing is to add the walls to the outside, S in m2.

U global = C / S in W / m2. ° C

For example: If S = 238 m2
U overall = 114/238 = 0,48 W / m2. ° C

7) your frame evolves.

If your frame changes, you can recalculate its need without having your DPE redone.
For example you insulate your ceiling of 75m2 having a U = 2,5 w / m2. ° C (without insulation). You put 30 cm of insulation lowering the U to 0,13 w / m2. ° C
Gain = Area x (old U - new U) x B x24 / 1000

For example: Gain = 75 x (2,5 - 0,13) x1800 x 24/1000 = 7879 kW.h

New annual final heating consumption = Old annual final heating consumption - Gain

8) Thermix

There is free software on the web that can compare your heating and domestic hot water solutions.
You already know your heating needs.
For your domestic hot water need, you will find it under the term Spouts on the last page. If your water heater is far from your bathroom, you will have an Rd (distribution efficiency) of 0,8. Your need for domestic hot water will therefore be Spouts / 0,8.

Attention Thermix asks for the energy yields of each solution. For a thermodynamic water heater, a reversible air conditioner or a heat pump, take the SCOP and multiply it by 100.

For example a SCOP of 5,2 corresponds to 520%

Good calculations everyone

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