Radiant heating seems no different than forced air

asked 2016-06-16 06:00:32 -0500

updated 2016-11-12 09:08:41 -0500

Dear UMH forum, I am evaluating my first energy model in which I compare radiant heating (ZoneHVAC:HighTemperatureRadiant) against non-radiant heating. The building is a sizeable (10k m2 / 100k sq.ft.) warehouse in ASHRAE Climate Zone 5a. The model is working with no evident problems and I am reporting:

  1. normal zone dry bulb temp
  2. operative temperature
  3. mean radiant temperature

As I review results, I notice: - the difference in these 3 temperatures for a winter DesignDay is tiny, a few tenths of a degree F. - the zone setpoint temperature is inexplicably different than my schedule (69.4F vs. 68F)

My understanding from radiant manufacturers is that acceptable comfort is maintained by radiant heating at significantly lower dry bulb temperatures - this does not appear to be the case in my model. (I "think" that the operative temperature is supposed to reflect the apparent comfort.) I have reviewed the I/O reference and a little of the Engineering Reference, but do not understand why the radiant system operates with so little difference between the various "types" of zone temperature.

Can you share insights, please?

p.s., there is an air loop which I have temporarily given very low capacity in order to see the impact of radiant more clearly.

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What type of thermostat do you use in the radiant case?

Julien Marrec's avatar Julien Marrec  ( 2016-06-16 06:53:04 -0500 )edit

ZoneControl:Thermostat Tstat_Warehouse:WhseZone Warehouse:WhseZone Sched_CtrlType1 ThermostatSetpoint:SingleHeating HtgSP_Warehouse:WhseZone

ThermostatSetpoint:SingleHeating HtgSP_Warehouse:WhseZone Sched_HtgSPWarehouse

ZoneControl:Thermostat:OperativeTemperature Tstat_Warehouse:WhseZone Constant 0.7

Jim Dirkes's avatar Jim Dirkes  ( 2016-06-16 07:32:07 -0500 )edit

Keep in mind also that the HighTemperatureRadiant object (like LowTemperatureRadiant) controls to its own setpoint and temperature control type, instead of the zone's.

Eric Ringold's avatar Eric Ringold  ( 2016-06-16 09:17:13 -0500 )edit

Eric, My earlier comment shows the controls I'm using. Are you saying those are incorrect?

Jim Dirkes's avatar Jim Dirkes  ( 2016-06-16 13:50:04 -0500 )edit

I'm saying radiant system models aren't influenced by the zone thermostat for temperature control. Instead, the 'Heating Setpoint Temperature Schedule Name','Heating Throttling Range', and 'Temperature control type' inputs to the HighTemperatureRadiant object are what determines the system response. The control scheme is described here for LowTemperatureRadiant, but applies to HighTemp as well.

Eric Ringold's avatar Eric Ringold  ( 2016-06-16 14:12:27 -0500 )edit