Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
This isn't an open studio specific answer, but in other tools like TRNSYS I've noticed that if you don't turn off the pump when the sun is down the collectors will lose considerable heat. That should be mitigated somewhat in an evacuated tube system, but I'd check the flow rate. You could also do a temperature based control where the pump doesn't startup until the panel temperature exceeds a desired set point.
Also if the flow rate is too high you won't see higher temperatures as the heat is carried away too quickly likewise if your inlet temperature is too low.
Also, in northern climates solar hot water systems are often drained at night into holding tanks so that the working fluid doesn't freeze. That may help overall performance.
Finally, the angle of the collector makes a difference too. The best angle for overall solar gain is not necessarily the best angle for your system. Try more vertical angles to get more consistent year round performance. The summer will be worse, but the rest of the year will be better.
Hope that makes sense.
