ᐅ Extremely High Pellet Consumption (200 kg in 3 Days) in a KfW 70 Multi-Family House!
Created on: 9 Nov 2016 14:35
R
rudiherbert
Hello,
I just noticed the following regarding our pellet heating system (6-family new build, KfW70 standard). This is a new build and the first winter...
The consumption in October (which was very mild here) was 1000 kg.
Currently, the consumption is 200 kg over 3 days!
Projected, that would be 2,000 kg per month!
Although temperatures have dropped somewhat, there is still no sign of a harsh winter.
Here is what I observed about the pellet heating system (Eta 20-30).
The underfloor heating temperature is 56°C (133°F) with an outside temperature of 1°C (34°F).
Supply temperature to the underfloor heating in the boiler room is only 30°C (86°F)? The return temperature is the same?
The supply temperature shown inside the apartment is 38°C (100°F) when the room thermostat is active, and 20°C (68°F) when inactive.
The buffer tank is supported by solar thermal collectors on the roof (for domestic hot water and heating).
I am certain that this consumption cannot be correct!
The new build is well insulated. The building is dry. Everyone heats reasonably and ventilates correctly.
2,000 kg of pellets per month in winter is extremely high!
In October, we used 1,000 kg.
In summer, about 500 kg per month.
Before contacting the heating technician or property management, I wanted to get some advice here.
Thank you.
I just noticed the following regarding our pellet heating system (6-family new build, KfW70 standard). This is a new build and the first winter...
The consumption in October (which was very mild here) was 1000 kg.
Currently, the consumption is 200 kg over 3 days!
Projected, that would be 2,000 kg per month!
Although temperatures have dropped somewhat, there is still no sign of a harsh winter.
Here is what I observed about the pellet heating system (Eta 20-30).
The underfloor heating temperature is 56°C (133°F) with an outside temperature of 1°C (34°F).
Supply temperature to the underfloor heating in the boiler room is only 30°C (86°F)? The return temperature is the same?
The supply temperature shown inside the apartment is 38°C (100°F) when the room thermostat is active, and 20°C (68°F) when inactive.
The buffer tank is supported by solar thermal collectors on the roof (for domestic hot water and heating).
I am certain that this consumption cannot be correct!
The new build is well insulated. The building is dry. Everyone heats reasonably and ventilates correctly.
2,000 kg of pellets per month in winter is extremely high!
In October, we used 1,000 kg.
In summer, about 500 kg per month.
Before contacting the heating technician or property management, I wanted to get some advice here.
Thank you.
@Saruss
He owns a multi-family house, so the consumer flow rate is many times higher than the heat generator flow rate.
The thermal energy from the generator is likely transferred to the underfloor heating system via a hydraulic separator.
Even though the heating curve should theoretically adjust to high supply temperatures at sub-zero temperatures, in practice, the maximum supply temperature at a professional level is probably limited to 45-55°C (113-131°F).
He owns a multi-family house, so the consumer flow rate is many times higher than the heat generator flow rate.
The thermal energy from the generator is likely transferred to the underfloor heating system via a hydraulic separator.
Even though the heating curve should theoretically adjust to high supply temperatures at sub-zero temperatures, in practice, the maximum supply temperature at a professional level is probably limited to 45-55°C (113-131°F).
@rudiherbert
This is theory versus practice.
Theoretically, you should get the following:
55 kWh/m² x 550 m² (5900 ft²) = 30,250 kWh/year
1 kWh = 0.2 kg pellets (0.44 lbs)
30,250 kWh/year x 0.2 kg pellets = 6,050 kg pellets (13,334 lbs)
This corresponds to:
January 23% -> 1.4 t (1.4 metric tons)
February 11% -> 0.67 t (0.67 metric tons)
March 8% -> 0.5 t (0.5 metric tons)
April 1% -> 0.06 t (0.06 metric tons)
May 0% -> 0 t
June 0% -> 0 t
July 0% -> 0 t
August 0% -> 0 t
September 0% -> 0 t
October 4% -> 0.25 t (0.25 metric tons)
November 11% -> 0.67 t (0.67 metric tons)
December 19% -> 1.15 t (1.15 metric tons)
Will it stabilize from the second year onwards? No idea.
This is theory versus practice.
Theoretically, you should get the following:
55 kWh/m² x 550 m² (5900 ft²) = 30,250 kWh/year
1 kWh = 0.2 kg pellets (0.44 lbs)
30,250 kWh/year x 0.2 kg pellets = 6,050 kg pellets (13,334 lbs)
This corresponds to:
January 23% -> 1.4 t (1.4 metric tons)
February 11% -> 0.67 t (0.67 metric tons)
March 8% -> 0.5 t (0.5 metric tons)
April 1% -> 0.06 t (0.06 metric tons)
May 0% -> 0 t
June 0% -> 0 t
July 0% -> 0 t
August 0% -> 0 t
September 0% -> 0 t
October 4% -> 0.25 t (0.25 metric tons)
November 11% -> 0.67 t (0.67 metric tons)
December 19% -> 1.15 t (1.15 metric tons)
Will it stabilize from the second year onwards? No idea.
rudiherbert schrieb:
The energy certificate states that the building should require 55 kWh of primary energy. That would be about 6 tons of pellets per year. Not almost three times that amount.Not at all. It’s already stated on page 1.
What you are looking for is the final energy demand. With this, you can calculate how much fuel you will need to heat the house and provide hot water.
The primary energy demand expands the formula to calculate the final energy demand by including the primary energy factor of the fuel. This factor expresses how much additional energy is used throughout the entire process chain to extract or produce the energy carrier. It is defined by standards and can vary. For example, mining coal is more energy-intensive than producing pellets. In addition, there is a political preference to burn domestic wood (because it is more climate-friendly) instead of Chinese lignite coal. Coal therefore has a factor of 1.1, wood 0.2. Electricity was rated at 2.4 until the end of 2015—which is rather unfavorable—and since early 2016 at 1.8. This means that heat pumps can achieve a lower primary energy demand, making it easier to meet standards such as KfW. This is a political decision. On the other hand, it also means that with a gas heating system, meeting the KfW 55 standard (just barely) is no longer possible without mixing in an additional renewable energy source (e.g., solar thermal).
If you take the final energy demand and multiply it by the primary energy factor, you get the primary energy demand. Specifically, the consumption you calculated based on the primary energy demand in tons of pellets must be divided by 0.2 or multiplied by a factor of 5 to make a consumption forecast based on the energy certificate.
Final energy Qe = Useful energy Qn + system losses
Primary energy Qp = Final energy Qe × fp
But putting the calculations aside, I’m still surprised by your "surprise."
If you consumed 0.5 tons per month in summer with support from solar thermal, an increase to 2 tons per month in the cold season is hardly surprising. After all, the heating system now needs to heat the house (which requires significantly more energy than hot water preparation) and provide hot water, which was previously (almost) entirely covered by the solar thermal system.
There have been heating load calculations mentioned in this forum that confirmed a heating load of 6 kW, about 1.5 kW of which is for hot water (if I remember correctly). Just to give you an idea of how much more demanding it is to heat the house compared to hot water preparation.
Wait until it gets really cold. It won’t stay at 2 tons per month.
AOLNCM schrieb:
55kWh/m² x 550m² = 30250 kWh/aThe equation cannot be correct because, on one hand, the primary energy demand was used as a consumption value, and on the other hand, the living area was applied, which is not appropriate. The area figures in the energy certificate refer to the total area within the heated envelope (calculated by multiplying the volume by a fixed factor). In other words, usable floor area. Of course, this is again quite imprecise, as the fixed conversion factor does not account for unusual or varying ceiling heights.
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