Hello everyone,
I need your advice: We contractually agreed with our main contractor that the Wolf gas-solar unit CSZ-2-14/300R would be installed in our house. This week, I accidentally discovered that instead, the next larger model, the CSZ-2-20/300R, has been installed. (The house is not finished yet; handover is expected in March.)
As the model names suggest, these units have maximum outputs of 14 kW and 20 kW, respectively. If I understand our energy saving certificate correctly, our house (energy saving regulations, 225 m² (2420 ft²)) has an annual heat demand of 14,987 kWh (11,681 kWh space heating, 3,306 kWh domestic hot water). Lacking technical expertise, I found during some initial research that I can estimate the heating load by dividing annual heating hours (about 2,100 h?) into this. Using this rough calculation, I arrive at a heating load of around 7.1 kW. Is this correct so far, and am I right to assume that this means the 20 kW version is significantly oversized?
Another problem is that the lower modulation limit of the larger boiler is much higher: 4.4 kW compared to 2.1 kW. I’m concerned that especially during transitional seasons, the boiler will cycle more frequently, leading to faster wear and less efficiency overall.
I haven’t been able to speak directly with the installer yet. The construction manager of the main contractor relayed the installer’s explanation that the unit was “sized larger due to the building size.”
I will discuss this with our independent construction expert next week.
So here are my questions:
Is my assumption correct that the 20 kW version is completely oversized?
Is my assumption correct that the higher lower modulation limit is a disadvantage for us?
How would you approach this situation? How serious do you see the issue, and what options do I have?
Thanks for your help
I need your advice: We contractually agreed with our main contractor that the Wolf gas-solar unit CSZ-2-14/300R would be installed in our house. This week, I accidentally discovered that instead, the next larger model, the CSZ-2-20/300R, has been installed. (The house is not finished yet; handover is expected in March.)
As the model names suggest, these units have maximum outputs of 14 kW and 20 kW, respectively. If I understand our energy saving certificate correctly, our house (energy saving regulations, 225 m² (2420 ft²)) has an annual heat demand of 14,987 kWh (11,681 kWh space heating, 3,306 kWh domestic hot water). Lacking technical expertise, I found during some initial research that I can estimate the heating load by dividing annual heating hours (about 2,100 h?) into this. Using this rough calculation, I arrive at a heating load of around 7.1 kW. Is this correct so far, and am I right to assume that this means the 20 kW version is significantly oversized?
Another problem is that the lower modulation limit of the larger boiler is much higher: 4.4 kW compared to 2.1 kW. I’m concerned that especially during transitional seasons, the boiler will cycle more frequently, leading to faster wear and less efficiency overall.
I haven’t been able to speak directly with the installer yet. The construction manager of the main contractor relayed the installer’s explanation that the unit was “sized larger due to the building size.”
I will discuss this with our independent construction expert next week.
So here are my questions:
Is my assumption correct that the 20 kW version is completely oversized?
Is my assumption correct that the higher lower modulation limit is a disadvantage for us?
How would you approach this situation? How serious do you see the issue, and what options do I have?
Thanks for your help
My gas boiler was turning on every 3 minutes... it would heat for about 1 minute and then shut off again... For example, the supply temperature was around 20°C (68°F) when the boiler started... then it heated the water to over 30°C (86°F) within less than a minute and switched off because the setpoint was reached or even exceeded... It only heats longer when all heating circuits are open, but even then it turns off after a few minutes. As soon as the heating stops, you can see the supply temperature drop rapidly again, resulting in the boiler restarting shortly afterward.
Modulation doesn’t even come into play, since that requires some time. And even if it did, the 7 kW output is still higher than the house heating load...
I have now activated a cycle restriction (every 10 minutes) and monitored the indoor temperature. We consistently have 22.5°C (72.5°F) in every room (my wife prefers it that way) and pay about 70 euros per month for gas. I can live with that for now... but I think there is still potential for savings. Also, around 100 burner starts per day can’t be good for the boiler...
A funny anecdote: When heating the screed, the boiler ran full power for about 3 weeks. My utility company’s bill for the period from mid-November to the end of December showed a gas consumption of around 900 m³. The utility representative said that’s actually very good for a single-family house per year... until I told her it was only 1.5 months. And in fact, my annual consumption is now about 950–1,000 m³ per year...
Modulation doesn’t even come into play, since that requires some time. And even if it did, the 7 kW output is still higher than the house heating load...
I have now activated a cycle restriction (every 10 minutes) and monitored the indoor temperature. We consistently have 22.5°C (72.5°F) in every room (my wife prefers it that way) and pay about 70 euros per month for gas. I can live with that for now... but I think there is still potential for savings. Also, around 100 burner starts per day can’t be good for the boiler...
A funny anecdote: When heating the screed, the boiler ran full power for about 3 weeks. My utility company’s bill for the period from mid-November to the end of December showed a gas consumption of around 900 m³. The utility representative said that’s actually very good for a single-family house per year... until I told her it was only 1.5 months. And in fact, my annual consumption is now about 950–1,000 m³ per year...
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