Hi,
I'm trying to model a VAV system for a house that has supply only in living/bedrooms and exhaust in kitcen/bathroom but unfortunately Apache won't let me simulate due to a "pressure exceeded" error from Macroflo. I have set some independent controllers with 0 flow-rate on the exhaust connector from the liv/bedrooms and also for the inlet of the kit/baths. The VAV is simulated through the independent controllers with sensor existing on the rooms with supply, the control of the flow-rate being varied according to a dry-bulb temp. proportional control setup. So is there a way around this because I'm sure is nothing wrong with macroflo since it works if I use only independent controllers, that is simulate a CAV sistem, which is not my case.
Thank you anticipated!
VAV with exhaust through kitcen and bathroom
Re: VAV with exhaust through kitcen and bathroom
For ApHVAC in combination with Macroflow, you will require an inlet and outlet, a room component, a fan component and two time switches set up to control flow rate. Position a time switch before and after the room component (intake and exhaust side) place the fan after the room component. The time switch on the inlet/ air intake should have the flow rate set to 0. The time switch on the outlet/ exhaust should have the flow rate set to the exhaust flow rate. By setting the intake flow to 0 you create an inbalance in the HVAC network. If you are using macroflo then it will try to balance airflow by drawing air through internal and external macroflo openings.
Re: VAV with exhaust through kitcen and bathroom
Yes that's exactly what I've done when I wanted to set a constant air flow for each room and then balance the exhaust air flow by using time switches and specifying the flow there. But the problem was when I wanted to simulate a changing air flow in each room, based on temperature sensors (independent controller with sensor - icws), because ApacheHVAC cannot calculate the varying exhaust air flow based on varying inlet air flow. It searches for openings in Macroflo instead of calculating like for example total_exhaust_air_flow_at_time_0_in kitcen+bathrooms = sum(airflow_at_time_0_in living room + air_flow_at_time_0_in bedroom) and therefore avoid the error in Macroflo. I've also seen that ApacheSim doesn't have any problems if icws are used on each room as long as time switches are not used at the same time on the exhaust branch. Altough that did not solve my problem since that would mean I have supply and exhaust in the same room which yields totally different results than when having exhaust only say in kitchens and bathrooms.
The only way I found around this is to define 3 independent controllers with sensor on the 3 exhaust branches coming from the 3 rooms that have exhaust (kitcen + 2 bathrooms) that varies the air flow based on sensed air flow on the main inlet branch. Although this is not a perfect solution because it only worked if I kept a 0.01% opening on windows such that a very small amount of air is drawn through windows when the exhausted air flow could not be exactly balanced with the varying inlet air flow.
It would be nice to have an update that would solve this balancing problem of inlet and outlet for ventilation systems with supply in some rooms and exhaust in different rooms other than in the ones with supply. I found it to be a very common situation since most of the time the supply and exhaust are not in the same room, but are on corridors or areas where the highest pollutant level is reached.
The only way I found around this is to define 3 independent controllers with sensor on the 3 exhaust branches coming from the 3 rooms that have exhaust (kitcen + 2 bathrooms) that varies the air flow based on sensed air flow on the main inlet branch. Although this is not a perfect solution because it only worked if I kept a 0.01% opening on windows such that a very small amount of air is drawn through windows when the exhausted air flow could not be exactly balanced with the varying inlet air flow.
It would be nice to have an update that would solve this balancing problem of inlet and outlet for ventilation systems with supply in some rooms and exhaust in different rooms other than in the ones with supply. I found it to be a very common situation since most of the time the supply and exhaust are not in the same room, but are on corridors or areas where the highest pollutant level is reached.