I am investigating an existing building. The idea is to add insulation and keep the existing baseboards. So, the (new) heating can work with a lower supply temperature.
When I autosize maximum (water) flow rates and/or UA-factors in the objects ZoneHVAC:Baseboard:Convective:Water, Boiler:HotWater and PlantLoop, I get a Delta T of the HW-loop up to 15 °K (which is fine).
Then I set myself maximum water flow rates for the baseboards (based on the maximum heating rates from a simulation), while keeping the flows of Boiler:HotWater and PlantLoop autosized. Delta T of the HW-loop dropped to about 3 °K (which is to small). The results for the Zone Mean Air Temperatures and Baseboard Heating Rates are still fine (and similar to the autosized situation). Apparently, the flow in the HW-loop is quite big now and most of the flow during most of the time is going through the bypass on the demand-side of the HW-loop. This increases the return temperature and decreases Delta T. A small Delta T is not economic.
The occuring maximum loop flow in the HW-loop is exactly the sum of all maximum water flows of all the baseboards (as specified in the object ZoneHVAC:Baseboard:Convective:Water). So, I tried to set myself a lower Maximum Loop Flow Rate of the Plant:Loop (in order to lower the bypassed flow and thus increasing Delta T). I choose the maximum sum of all the baseboards water flows AT ANY GIVEN MOMENT. This maximum is --in my case-- less then half of the sum of all (non-simultaneously) maximum water flows. And, by the way, about twice as much as for the completely autosized situation.
But even when I manually set the Maximum Loop Flow Rate of the Plant:Loop, the occuring flow in the HW-loop is still the (much higher) sum of all (non-simultaneously) maximum flows of all baseboards.
Did I forgot to change another object too or is this a bug?
PS. I tried to attach the idf-file but could not find the way to do this.