[bldg-sim] Overhead Radiant Heaters

[Alex Harvey]

Steve makes a very incisive point.

Where comfort is largely due to radiant heat a very unstable situation can
result.

One only has to spend a day at the beach and observe the reaction of
holiday-makers when the sun disappears behind a cloud to vindicate this.

The time constant for radiant heat is desperately short compared to that of
the ambient temperature as determined by a thermostat. The resultant
oscillation in radiant heat provision could prove to be at no point
comfortable.

Alex Harvey

----- Original Message -----
From: "Steven Gates" <steve.gates at doe2.com>
To: <bldg-sim at gard.com>
Sent: 28 October 2005 16:53
Subject: [bldg-sim] Overhead Radiant Heaters


> Interesting discussion; the reasons given for radiant in a high-bay
> environment pertaining to stratification/infiltration make a lot of sense.
>
> I have a related question:  How is radiant heat typically controlled in
> either a high-bay environment or a residence?  The controls I have seen in
> radiant systems appear to be on/off thermostats (I haven't seen many
> systems).  I have heard the argument that the temperature setpoint can be
> dropped a few degrees, but don't understand how that actually works with
an
> on/off controller.
>
> For example, assume that the space is comfortable at 65F when the radiant
> heat is on.  Also assume that the temperature in the current hour is 66F.
> Given the temperature, is the radiant heater off?  If so, then there is no
> radiant heat effect and the space might be uncomfortable; causing the
> occupants to raise the setpoint.  The net effect is that, over time, a
> radiant system could wind up having the same setpoint as a convective
> system.
>
> A more sophisticated way of controlling the space would be to implement a
> modulating control, but I do not know whether this is commonly done.  This
> type of system would need to start adding heat at the same setpoint as a
> convective system, but not in sufficient quantity to maintain the
setpoint.
> More heat would be added as the space temperature continued to droop,
until
> equilibrium is achieved around 65F.
>
> Is anyone aware of field studies comparing the actual setpoints used with
> radiant vs. convective heating in similar environments, where the
occupants
> are "uneducated" regarding radiant heating's "benefits"?
>
> Steve Gates
>
>
> -----Original Message-----
> From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of Jon
Maxwell
> Sent: Friday, October 28, 2005 7:51 AM
> To: bldg-sim at gard.com
> Subject: [bldg-sim] Overhead Radiant Heaters
>
> I think you're on the right track.  I don't have a paper to offer, just an
> opinion that I have loosely correlated with field observations.  Reduce
the
> temperature for two reasons:  (1) People are comfortable at a lower
> temperature with radiant than convection heating.  So reduce your modeled
> inside setpoint a couple of degrees on account of that.  (2) Radiant
> delivers major stratification-related savings as well.  With a 40- to
50-ft
> ceiling and forced air heat, you might have to maintain 90F air at ceiling
> in order to have 70F air at the 5-ft high thermostat.  That means the
> average inside temperature is 80F even if the setpoint is 70F.  Radiant
> won't have that problem.  So that would be another 10F reduction on the
> average inside temperature.
>
> Third, by eliminating the aforementioned stratification you will reduce
the
> stack effect-driven infiltration.  This can have a measurable effect on
the
> heating load if your building is not pressurized with a lot of OA.
>
> Fourth, check your candidate equipment rated efficiencies.  Depending on
> venting and burner types a radiant heater can be more efficient than a
> convection unit.
>
> Jon Maxwell
> Aspen Systems
>
> ----- Original Message -----
> From: "Mike Tillou" <miket at etcgrp.com>
> To: <bldg-sim at gard.com>
> Sent: Friday, October 28, 2005 10:04 AM
> Subject: [bldg-sim] Overhead Radiant Heaters
>
>
> Hi all,
>
> I am currently modeling an overhead radaiant heating system in a large
> industrial building.  The application is similar to a Public Works
> garage, large overhead clearence (50' center height), insulated metal
> building, space doesn't have to be heated but they need heating for
> employees at the ground level.
>
> I plan on using DOE2.2 because I don't have the budget for using a more
> appropriate modeling tool.
>
> Does anyone have good ideas about how to approach this using a DOE 2.2
> model?
>
> My initial thoughts have focused on reducing the space temperature
> setpoint but how much is appropriate 2 degrees , 5 degrees or 10 degrees
> ?   Are there any papers or articles that discuss air temp vs mean
> radiant temp of the surrounding mass while using overhead radiant
> heaters?
>
> Many thanks in advance for any help/guidance that can be offered.
>
> Mike
>
>
> Michael Tillou, PE
> etc Group, Inc.
> PO Box 7, Williamstown, MA 01267
> ph. (413) 458-9870 fx. (413) 458-9875
> www.etcgrp.com
>
>
>
>
>
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