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
H
hampshire1 Mar 2020 11:22Modern gas heating systems operate with regulation and not just at full power. It is also known today that you should not simply turn off radiators arbitrarily. With a proper hydraulic balancing, oversizing should neither significantly affect costs nor the system’s lifespan. After all, it’s not a heat pump.
Address the issue, agree on a solution (discount or additional service), and stay positive.
Address the issue, agree on a solution (discount or additional service), and stay positive.
No worries, I am familiar with the HTD forum. If in doubt, I would also ask there.
I understand that modern boilers modulate — I guess that’s what you meant by “regulated operation,” @hampshire. But if the installed heating system only modulates down to a minimum of 4.4 kW (15,000 BTU/h), while the house has a heating load of only 7 kW (24,000 BTU/h), I do wonder how often it won’t be able to modulate low enough and will start short cycling.
For now, I will first discuss this with the installer, site manager, and building inspector to find out how big an issue this actually is. Of course, I don’t want to raise a fuss before that. The construction so far and communication with the builder have always been extremely pleasant, fair, and solution-oriented, so I expect we will find a good agreement here as well.
I understand that modern boilers modulate — I guess that’s what you meant by “regulated operation,” @hampshire. But if the installed heating system only modulates down to a minimum of 4.4 kW (15,000 BTU/h), while the house has a heating load of only 7 kW (24,000 BTU/h), I do wonder how often it won’t be able to modulate low enough and will start short cycling.
For now, I will first discuss this with the installer, site manager, and building inspector to find out how big an issue this actually is. Of course, I don’t want to raise a fuss before that. The construction so far and communication with the builder have always been extremely pleasant, fair, and solution-oriented, so I expect we will find a good agreement here as well.
H
hampshire1 Mar 2020 16:00You are right, the minimum power output at startup does matter.
That speaks well of you too.
opalau schrieb:
The construction so far and the communication with the building company have always been extremely pleasant, fair, and solution-oriented. I expect that we will reach a good agreement here as well.
That speaks well of you too.
So, we also have a gas heating system, but only for 165 sqm (1776 sq ft). We have a Buderus with a total output of 14 kW (14,000 BTU/hr), and it can modulate down to 14%, which corresponds to about 2 kW (6,800 BTU/hr).
I just checked since it’s running right now. It’s 7°C (45°F) outside, and the system is producing a flow temperature of 24–25°C (75–77°F). At the moment, it is modulating at 15%.
Since your larger heating system has twice the output, it would run for shorter periods and cycle more frequently. I have logged 2,107 operating hours and 1,287 burner starts, which averages about 1.6 hours per start. On cool days, I only need 2–3 starts per day.
I would definitely try to get the smaller system.
I just checked since it’s running right now. It’s 7°C (45°F) outside, and the system is producing a flow temperature of 24–25°C (75–77°F). At the moment, it is modulating at 15%.
Since your larger heating system has twice the output, it would run for shorter periods and cycle more frequently. I have logged 2,107 operating hours and 1,287 burner starts, which averages about 1.6 hours per start. On cool days, I only need 2–3 starts per day.
I would definitely try to get the smaller system.
Approximately 7 kW should be suitable based on the heating load. This is calculated using the standard outdoor temperature, which will likely be around -10°C (14°F) depending on the location. Accordingly, you will need even less heating capacity most of the time.
Even if the system is oversized, you will probably have to accept it. No one will pay for a replacement. Also, the originally planned system was already too large.
For gas heating, this is not a major issue. For heat pumps, however, this is a no-go.
A 20 kW boiler in a single-family house still comes from the time of oil boilers and gas heaters without condensing technology. This indicates an incompetent company.
Even if the system is oversized, you will probably have to accept it. No one will pay for a replacement. Also, the originally planned system was already too large.
For gas heating, this is not a major issue. For heat pumps, however, this is a no-go.
A 20 kW boiler in a single-family house still comes from the time of oil boilers and gas heaters without condensing technology. This indicates an incompetent company.
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