[bldg-sim] Radiant Heating/Cooling

[Alec Stevens]

Steve
My 2c:
One aspect that should save energy on a radiant hydronic system is that your
supply and return water temps are lower year round than in a typical
convective system.  If you consider a condensing hydronic boiler, you should
always be in condensing mode with radiant heat, but your HW reset schedule
for other forms of hydronic heat would mean you would not be condensing
except when OA temps are relatively high (Above 40F?).  Therefore, boiler
efficiency should be better with radiant for most of the heating season.

You raise some good points about the other issues.  I've only heard the
lower space temperature setpoint argument when it comes to spaces like
manufacturing areas, ice rinks, airplane hangars, etc.  Don't think it would
apply so much to residential, especially if you are going to cycle zone
valves on and off.  Modulating zone valves?



Alec

----- Original Message ----- 
From: <stvgates at pacbell.net>
To: <bldg-sim at gard.com>
Sent: Tuesday, April 13, 2004 11:48 AM
Subject: [bldg-sim] Radiant Heating/Cooling


> I also have some questions on radiant heating that I hope someone can
> answer:
>
> 1.  It is well understood that, for a given comfort level, a higher mean
> radiant temperature allows for a lower ambient temperature.  This suggests
> that one can lower the thermostat setpoint.  But, if the thermostat is
> lowered to 65F, and the ambient temperature is 66F, then the radiant heat
is
> off, and the mean radiant temperature drops.  So are the people
comfortable
> when the space is 66F, or do they raise the thermostat?
>
> 2.  Granted, infiltration heat losses can be lowered by reducing the air
> temperature.  But the radiant heat source is also warming the room
surfaces,
> including the exterior wall surfaces and window surfaces.  If those
surface
> temperatures are then higher than they would be with a convective heating
> system, their conduction losses are now greater, even though the air
> temperature is lower.  Also, infiltration/exfiltration losses are
typically
> through cracks.  If the cracks in the interior surfaces are warmer from
> radiant heating, then the crack warms the exfiltrating air, and space
> temperature is not a valid criterion for calculating exfiltration loss.
So
> does a radiant heating system REALLY save any energy?
>
> 3.  If the radiant elements are imbedded in the ceiling, which is common,
> the interior ceiling temperature can now be in excess of 90F, which
> increases the conduction losses to the attic.  So if this loss is counted
as
> a delivery loss, the efficiency of the system drops compared to the
> theoretical.  The same argument applies to radiant elements in floors.  So
> is a radiant system REALLY any more efficient than a convective system in
> terms of delivered energy?
>
> 4.  With a setback thermostat and a convective heating system, I can turn
> off the heat at night, but my home will be comfortable in less than a 1/2
> hour the next morning.  But most radiant heating systems have a slow
> response time.  Do people turn them off/down at night, or do they run them
> continuously?
>
> ----- Original Message ----- 
> From: "Jon Maxwell" <jmaxwell at aspensys.com>
> To: <bldg-sim at gard.com>
> Sent: Monday, April 12, 2004 8:46 PM
> Subject: [bldg-sim] Radiant Heating/Cooling
>
>
> > I have modeled the savings for radiant systems for unvented low
intensity
> > gas fired radiant tube heating systems in high bay warehouses and
> > manufacturing facilities in particular by:
> >
> >     1. Reducing the setpoint dry bulb temperature a few degrees because
> > human comfort with radiant heating is reached at a lower ambient than
with
> > convection heating systems.  I am certain that comfort research supports
> > this.
> >     2. Reducing the setpoint temperature a few more degrees because
there
> is
> > less floor-to-ceiling temperature stratification. With the desired
> > temperature at belly button level, radiant systems will have a lower
> average
> > temperature floor-to-ceiling than unit heaters overall.
> >     3. Reducing the amount of infiltration, due to reduced stack effect,
> due
> > to reduced temperature stratification
> >     4. Increasing the heating system combustion efficiency slightly due
to
> > having no intermediate media such as air or water between the combustion
> air
> > and the space to be heated and lack of venting.
> >
> > While I cannot cite studies to validate the adjustments or quantify them
> > generally (though I have rules of thumb based on ceiling height), such
an
> > approach has predicted savings roughly in the right ballpark, close
enough
> > to make a do/don't do decision at least.
> >
> > Would love to be able to cite rigorous research that proves or disproves
> my
> > approach.
> >
> > Jonathan B. Maxwell, PE
> > Senior Engineer
> > Aspen Systems Corporation
> > 710 Park Place
> > College Station, TX 77840
> > (979) 764-6779 wk
> > (979) 764-7810 fax
> > (979) 575-1281 mobile
> > jmaxwell at aspensys.com
> > www.OPUSPOWER.com
> > www.aspensys.com
> >
> > ----- Original Message ----- 
> > From: "Chris Jones" <cj at cr-jay.ca>
> > To: <BLDG-SIM at gard.com>
> > Sent: Monday, April 12, 2004 6:25 AM
> > Subject: [BLDG-SIM] Radiant Heating/Cooling
> >
> >
> > In your research with radiant heating cooling savings, have you found
any
> > energy "savings" that can be attributed directly to the use of the
radiant
> > system vs other systems (air supply in particular).  For example, I have
> > seen some papers that note that the heating setpoint can be relaxed
while
> > still maintaining thermal comfort with a radiant system.
> >
> >
> > At 10:47 07/04/2004, you wrote:
> > >Dear All,
> > >
> > >For those interested in the simulation of radiant heating/cooling
> systems,
> > >IRC has developed a semi-analytical model for integration in energy
> > >simulation software that use the one-dimensional numerical modeling to
> > >calculate the heat transfer within the building construction
assemblies.
> > >
> > >The model combines the one-dimensional model of the energy simulation
> > >software with a two-dimensional analytical model.  The advantage of
this
> > >model over the one-dimensional one is that it accurately predict the
> > contact
> > >surface temperature of the circuit-tubing and the adjacent medium,
> required
> > >to compute the boiler/chiller power, and the minimum and maximum
> > >ceiling/floor temperatures, required for local moisture condensation
> > >(ceiling cooling systems), thermal discomfort (heating floor systems)
and
> > >controls.  The model predictions for slab-on-grade heating systems
> compared
> > >very well with the results from a full two-dimensional numerical model.
> > >
> > >The model was implemented in the Canadian software HOT3000 and the UK
> > >software ESP-r as a plant component. The implementation of this model
in
> > the
> > >ESP-r program offers additional flexibilities to the radiant system
> > designer
> > >community, mainly:
> > >·       Designers can use any control algorithm possible in ESP-r with
> the
> > >new plant component (e.g.., use the flux or temperature control, and
> > compare
> > >their performance).
> > >·       Designers can specify any number of radiant surfaces of the
> > building
> > >fed by the same or different heat source.
> > >·       Designers can size realistic radiant systems, and get realistic
> > >energy consumption (from the source side) and cost.
> > >
> > >
> > >A copy may be downloaded from:
> > >Laouadi, A. "Development of a radiant heating and cooling model for
> > building
> > >energy simulation software," Building and Environment, 39, (4), April,
> pp.
> > >421-431, Apr, 2004
> > >(NRCC-46099)
> > ><http://irc.nrc-cnrc.gc.ca/fulltext/nrcc46099/>
> > >
> > >
> > >Thanks
> > >
> > >Dr. Abdelaziz (Aziz) Laouadi
> > >Research Officer
> > >Indoor Environment Research Program
> > >Institute for Research in Construction
> > >National Research Council of Canada
> > >1200 Montreal Road, Building M-24
> > >Ottawa, Ontario, Canada, K1A 0R6
> > >Tel.:  (613) 990 6868;  Fax:  (613) 954 3733
> > >Email: Aziz.Laouadi at nrc-cnrc.gc.ca
> > >Web: http://irc.nrc-cnrc.gc.ca/ie/light/skyvision/
> > >
> > >
> > >You received this e-mail because you are subscribed
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> >
> >
> > Chris Jones, P.Eng.
> > 14 Oneida Avenue
> > Toronto, ON M5J2E3
> > Tel. 416 203-7465
> > Fax. 416 946-1005
> >
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