ᐅ Increase the supply temperature from 40°C to 35°C or not?
Created on: 5 Mar 2022 00:47
H
HoisleBauer22
Hello everyone,
My home construction company specified a flow temperature of 40 degrees Celsius (104°F) in the contract "to save money," meaning a larger pipe spacing, probably increasing from 10-15 cm (4-6 inches) to 20 cm (8 inches).
The key data for the house (planned): KfW 55 standard, Daikin Altherma 3 R ECH2O 308/508, annual performance factor around 4, living area 145 m² (1560 ft²) with the basement also heated (this was required for KfW), the basement itself has 80 m² (860 ft²) of usable/floor space, but is not considered living space according to standards due to insufficient natural light.
We have a controlled ventilation system with heat recovery. We also plan to install a photovoltaic system of about 10 kW peak on the roof at some point.
Now I’m wondering if it would be worthwhile to reduce the flow temperature from 40 degrees Celsius (104°F) to 35 degrees Celsius (95°F) given an assumed electricity price of around 45 cents per kWh. The additional costs are about €15 per m² for the upgrade. The crucial point is how much energy savings percentage is achieved per degree of reduction. It is usually assumed to be 2.5 percent per degree, which would amount to 10–12.5 percent savings at 5 degrees lower flow temperature.
Does anyone have any ideas on how to calculate this or if there is a website available for such calculations?
My home construction company specified a flow temperature of 40 degrees Celsius (104°F) in the contract "to save money," meaning a larger pipe spacing, probably increasing from 10-15 cm (4-6 inches) to 20 cm (8 inches).
The key data for the house (planned): KfW 55 standard, Daikin Altherma 3 R ECH2O 308/508, annual performance factor around 4, living area 145 m² (1560 ft²) with the basement also heated (this was required for KfW), the basement itself has 80 m² (860 ft²) of usable/floor space, but is not considered living space according to standards due to insufficient natural light.
We have a controlled ventilation system with heat recovery. We also plan to install a photovoltaic system of about 10 kW peak on the roof at some point.
Now I’m wondering if it would be worthwhile to reduce the flow temperature from 40 degrees Celsius (104°F) to 35 degrees Celsius (95°F) given an assumed electricity price of around 45 cents per kWh. The additional costs are about €15 per m² for the upgrade. The crucial point is how much energy savings percentage is achieved per degree of reduction. It is usually assumed to be 2.5 percent per degree, which would amount to 10–12.5 percent savings at 5 degrees lower flow temperature.
Does anyone have any ideas on how to calculate this or if there is a website available for such calculations?
H
HoisleBauer227 Mar 2022 21:56I would like to return to my calculation.
Note: For 20 years, that means about €2,800 (from 40 to 35) or about €5,600 (from 40 to 30) savings versus a price premium of €3,375 - €4,500 (€15-20/m²).
Can it be assumed that the energy savings from 40 to 35 (10-12.5%) are proportional to 40 to 30 and thus amount to 20-25%?
I wonder: Where does the value of 2-2.5% savings per degree even come from?
HoisleBauer22 schrieb:
A calculation attempt:
If I assume a heat demand of 55 kWh/a m² and an area of 225 m² (including the basement, even though it is not living space!), that results in 12,375 kWh per year. With an annual performance factor of about 4, this means 12,375 ÷ 4 = 3,094 kWh of electricity consumption. Assuming electricity costs of 45 cents per kWh, this amounts to roughly €1,392 in electricity costs. So, with a 10% energy savings (about 2% per degree) due to a lower supply temperature (35 degrees), I would save around €139. The investment would only pay off in about 24 years. Probably not even then, since about 30% of my electricity/heat demand would be covered by photovoltaics and the electricity costs saved would be less than that.
Note: For 20 years, that means about €2,800 (from 40 to 35) or about €5,600 (from 40 to 30) savings versus a price premium of €3,375 - €4,500 (€15-20/m²).
Can it be assumed that the energy savings from 40 to 35 (10-12.5%) are proportional to 40 to 30 and thus amount to 20-25%?
I wonder: Where does the value of 2-2.5% savings per degree even come from?
R
RotorMotor7 Mar 2022 23:23HoisleBauer22 schrieb:
Is it reasonable to assume that the energy savings from 40 to 35°C (104 to 95°F) — which is about 10–12.5% — scale proportionally to the savings from 40 to 30°C (104 to 86°F), meaning 20–25%? No, that is not the case.
HoisleBauer22 schrieb:
I wonder: Where does the figure of 2–2.5% savings per degree come from? From the "Internet." It is quite likely only valid at very high supply temperatures.