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
Hello,
This probably won’t work because the storage tank of the system only has a standby capacity of about 120 liters (32 gallons).
Imagine using a rain shower with a flow rate of 36 liters per minute (9.5 gallons per minute) on this 14 kW system. The tank will be empty after just a few minutes. If someone in the guest apartment has just prepared a bath, you’ll end up showering with cold water immediately after.
In the end, it depends on the flow rate of the water heater, and it may be necessary to adjust the output of the heat generator accordingly.
Olli
This probably won’t work because the storage tank of the system only has a standby capacity of about 120 liters (32 gallons).
Imagine using a rain shower with a flow rate of 36 liters per minute (9.5 gallons per minute) on this 14 kW system. The tank will be empty after just a few minutes. If someone in the guest apartment has just prepared a bath, you’ll end up showering with cold water immediately after.
In the end, it depends on the flow rate of the water heater, and it may be necessary to adjust the output of the heat generator accordingly.
Olli
I find this embarrassing for the company.
What really matters, as you’ve recognized, is the lower limit of modulation. With the current system, you will definitely need to carry out both hydraulic and thermal balancing to minimize short cycling. Even with gas, wear increases in an on/off configuration. While this does not immediately affect consumption, it does impact maintenance costs.
By the way, I wouldn’t compare domestic hot water for a football club. But even if you do, it’s worth investing a bit more. In that case, simply use a large storage tank with a fresh water station. Do not integrate the storage tank hydraulically into the heating circuit.
This way, you have plenty of clean hot water available.
What really matters, as you’ve recognized, is the lower limit of modulation. With the current system, you will definitely need to carry out both hydraulic and thermal balancing to minimize short cycling. Even with gas, wear increases in an on/off configuration. While this does not immediately affect consumption, it does impact maintenance costs.
By the way, I wouldn’t compare domestic hot water for a football club. But even if you do, it’s worth investing a bit more. In that case, simply use a large storage tank with a fresh water station. Do not integrate the storage tank hydraulically into the heating circuit.
This way, you have plenty of clean hot water available.
I would recommend having it replaced; otherwise, it cycles constantly. We have a Junkers gas boiler with 24 kW (32,500 BTU/h) installed. The heating load is somewhere between 5-6 kW (17,000-20,500 BTU/h). The lowest modulation value is 7.3 kW (24,900 BTU/h). The positive aspect is that I have never run out of hot water.
I also trusted the heating engineer, whose exact words were: "We install these all the time, they fit well and last forever." I only noticed the issue much later when I kept wondering why it turns on and off so frequently.
Another side effect is that if I decide to build a multi-family house on my property later, I won’t need to replace the boiler. Everything fits perfectly as it is now.
I also trusted the heating engineer, whose exact words were: "We install these all the time, they fit well and last forever." I only noticed the issue much later when I kept wondering why it turns on and off so frequently.
Another side effect is that if I decide to build a multi-family house on my property later, I won’t need to replace the boiler. Everything fits perfectly as it is now.
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