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@nancynanxiaodan

Based on what I see, the radiators in the first floor bedroom is not able to meet the heating loads during the winter days. Hence the zone mean air temperature during the winters is not able to reach 25°C. This coupled with low inside surface temperatures for the zones results in low zone operative temperatures during the winter months. The zone tempeatures seem to be within the expected range during summer.

I see two solutions for this -

1. You can improve the envelope thermal properties so that the winter temperatures can be taken care of
2. increase the temperature set point for the hot water supply to the radiators

I increased the hot water supply temperature set point to 69°C from 55°C (max tank temperature that you have is 70°C and hence the max value that i chose was 69°C). The graphs now look like this:

Practical solutions like adding internal heat gains or having winter setbacks can also help but it looks like you were trying to evaluate a hypothetical scenario as you edited the OA drybulb temperature.

Hope that helps!

Cheers,

Raghu