# Proper blending: gas radiant heating & gas makeup / ventilation

Caveat: I am not too familiar with the physics of radiant heating, especially when combined with a typical air system.

The design I want to model uses gas radiant (overhead) heaters with an air loop gas heating system. The radiant heaters are intended to provide comfort; the air loop provides ventilation air for the entire building PLUS a reduced level of heating for the portions of the building which don't have radiant heat. It seems to me that I can use zone radiant heaters for the portions of the building that need comfort and an air loop for the rest of it, then use a ZoneCrossMixing object to "share" air between these zones.

Other notes:

• I intend to control the radiant system using Operative Temperature and the air loop by air temperature. (This strikes me as a potential problem of the systems "fighting" each other, but, as mentioned, I'm not too familiar with these concepts inside E+.)
• The "zones" are not separated physically by walls; it's a big warehouse in which people are normally in only portions of the building
• There are occupied and unoccupied periods during which the zone setpoint temperatures are different
• The radiant system is considered by ASHRAE to be a "low temperature" radiant system, but I'm assuming that E+ will model it well as long as I assign the proper combustion efficiency and radiant fraction
• There is no mechanical cooling system

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How is your air loop controlled? SAT?

How is this low temperature radiant if it's gas?

( 2016-06-06 05:51:04 -0500 )edit
1. Zone temperature control for the air loop

2. The only gas radiant object in E+ is ZoneHVAC:HighTemperatureRadiant, so that's my only choice (I think). As mentioned earlier, it seems that if I assign correct combustion efficiency and radiant fraction, it should be OK. Que pense?

( 2016-06-06 06:16:06 -0500 )edit

I think all gas radiant are necessary high temperature in the E+ sense (high intensity, the source of radiant heat is high temperature)

Is your airloop using recirculated air then? And what terminals do you have? VAV? Reheat/noreheat? Trying to understand what you mean by zone temperature.

Also, in a zone where you have both an airloop terminal and a radiant heater, what's the control sequence?

( 2016-06-06 06:22:13 -0500 )edit

Bottom line you can use one air loop and as many zone hvac components as you want. So I'd say use the airloop to serve all the zones that are really served, and also use a ZoneHVAC:HighTemperatureRadiant for the zones that do have it. The devil will be in the controls for zones where you have both.

( 2016-06-07 01:31:09 -0500 )edit

Thanks, Julien.

• Recirculated air and constant volume with no reheat
• The control sequence is still under discussion, but I think it will become something like using the air loop for "neutral" temperature discharge and the radiant heat for maintaining an comfortable operative temperature
• I agree that the difficult part will be controls; we'll see how it goes.
( 2016-06-07 07:38:57 -0500 )edit