Overlapping heating and cooling control temps in radiant system

asked 2015-07-23 08:18:05 -0500

Yan
1181 ●3 ●14 https://www.linkedin.c...

updated 2015-07-23 08:39:40 -0500

I tried to set up radiant heating and cooling system with regular VAV using OpenStudio 1.7. When I run the simulation, there is an error "Overlapping heating and cooling control temps in radiant system". I adjusted the cooling and heating T of radiant heating/cooling system, but it didn't work. Have you ever experienced this error? Or is there anything else I need to take care of when I build the radiant heating/cooling system with VAV? Thanks.

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answered 2015-07-23 08:31:52 -0500

ericringold

10527 ●31 ●8 https://www.nrel.gov/b...

You're seeing this error because the heating set point temperature plus half of the heating control throttling range is greater than the cooling set point temperature minus half of the cooling control throttling range. From the input reference, the temperature set point defined in the schedule is the temperature at which the system is at half of the maximum flow rate, and the throttling range defines the range of temperatures around that set point where the flow will modulate from zero to maximum. If your control points are calling for some flow for heating at a temperature above where they're also calling for some flow for cooling, the system can't make sense of this condition and will error.

If your scheduled set point temperatures are fairly close, I would reduce the heating and cooling control throttling ranges, or increase (and/or decrease) the cooling (and heating) set point temperatures.

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For the zone thermostat, I used regular numbers as before, 75F for cooling and 72F for heating. For VAV systems, supply air T is 55F as usual. It didn't cause any problem before I added radiant heating/cooling system. Actually, I directly used the "Low Temp Radiant Var Flow" from OS library and default setpoint and schedules for it. The "heating control temperature" for radiant heating is 122F as default, and "cooling control temperature" for radiant cooling is 59F as default. Are those resonable numbers?

Yan ( 2015-07-23 08:48:03 -0500 )edit

The radiant systems will reference their own temperature set point schedule objects, rather than the zone thermostat set point schedules, for control. The default schedules "Var Vol Rad Clg Air Temp Sch" and "Var Vol Rad Htg Air Temp Sch" don't appear to be reasonable, and indeed set up to cause the error that you received, since heating set point > cooling set point. I would change those schedule set points to be the same as your zone thermostat set points, e.g. 75F for cooling and 72F for heating.