Radiant Floor Cooling

wetheat1

I have a client that wants to explore the possibilities of radiant cooling using an existing heating system. It is 10k sqft slab on grade with 5/8" tubing 12" on center. Is there a way to work this backwards from the heating system design? Does anyone have the calculations for this application? What kind of controls are available? Thanks in advance.

WH1

Mike T., Swampeast MO

It all exists

Do some searching for "dewpoint sensors" and the like.

The MAJOR consideration is climate. Much of the US is too warm and humid for practical radiant cooling.

In the places where it is most practical, evaporative cooling (swamp A/C) is already in frequent use and much simpler and less expensive.

RB

use the search option on this site

for "radiant cooling"...past post are listed and you may get your answer...if not keep asking.

RB

Dave_4

rad cooling in humid climates

if the space is reasonably airtight humidity can be limited by pressurizing with dry ventillation air....use the chilled water in a fancoil before it hits the floor and dump 15-20 cfm of 54 degree air per person into the space (may also need a reheat coil to prevent overcooling)....equalize with relief/exhaust to prevent infiltration and extract any humidity generated by the occupants.....rad cooling works best against direct solar heat gain vs. cooling against internal loads like lights, people, equipment....no colder than 66 degree floor surface temp, and carpet has a much greater effect on rad cooling than heating.....no carpet if possible....reset temperature of constant flow chilled water into the floor based on space temp sensors with the dewpoint sensor at slab surface controling the fancoil supply air temp....try & zone interior/north, south/east & west separately (works in northern california)

RB

Where are you from J?

Well said information...

Some other things the Wallies might consider, as this radiant cooling develops in North America.

The convective cooling component on a radiant floor can be enhanced through the installation of ceiling fans... in radiant ceiling cooling you have natural currents working for you which is one of the reasons radiant chilled ceilings work better than radiant cooled floors...but the ceiling fans can create forced convection across the panel plus evaporative cooling from the body...both can greatly improve the performance...with a penalty in comfort in some cases.

If memory serves me...the very large Bangkok Airport, radiant cooled floor designed by Simmonds et al used a highly reflective ceiling so that radiant energy could be bounced off the ceiling back into the floor for absorption, thus reducing the building mass heat gains and improving the wire to water efficiency of the system.

The humidity challenge is to separate the sensible load from the latent load...the latent load is the heat carried in the air's moisture which can be condensed out on a chilled water coil mounted in the ventilation system. As J pointed out this can sometimes lower the air temperature below comfort conditions which is why you may need a re-heat coil in the summer...however this reheat coil could actually be a heat pipe air to air exchanger which not only addresses ventilation it also provides reheat if necessary.

Incidentally, ASHRAE have a $100,000 proposed research project based on hybrids, and a recent government report on top solutions to improving building efficiencies had radiant cooled ceilings as a top solution...something John Fantuzzi should know about to counter the less than perfect research work being done by the NAHB...John F are ya out there?

Radiant Comfort IAQ Systems ...keep your eyes on your fries...

RB

Mark Eatherton1

Wire to water efficiencies...

Nice term Robert. Good to see your words my friend.

I think Siggy just recently wrote something about wire to water efficiency. Good stuff. Something we need to pay more attention to, for sure.

ME

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Aidan (UK)

radiant cooling

The main difficulty is the change in the relative humidity caused by cooling the air. Cooling the air in the room will cause the relative humidity to increase, although the air’s moisture content ( in gms of water per kgm of air) will stay the same. Relative humidities of 80% could easily be achieved and is very uncomfortable. A psychrometric chart will make this clear.

The usual approach, for offices, is to dehumidify the ventilation air required to maintain the IAQ, at a central air handler. The radiant cooling surfaces have to be maintained at a temperature above the dew-point.

I stopped-off at Bangkok airport years ago. I was a bit baffled by water running down the outside of the windows, but didn’t have time to look. I don't know whether it was condensing humidity, a cooling system or window washing time. I wonder if that was the same building as the one that Robert Bean refers to; I’ll have to research this on Google. If radiant cooling can be made to work in Thailand’s humidity, it should work anywhere.


Search for radiant cooling at

http://epb1.lbl.gov/thermal/hydronic.html

Bob Gagnon plumbing and heating

radiant cooling

works great in northern mass. I simply run 56 degree well water through a flat plate exchanger and cool off my radiant floors to 68 degrees, i also have cool water run through a fan coil unit for additional cooling, air movement and some dehumidification. the humidity levels do go up as it gets cooler in the house but it is very comfortable, 70 degrees, and thats too cold for some people. i think having cooled floors are more effective than a lot of people think because you are in direct contact with the floor. walk on your cool tiles this time of year and see how fast you cool down, it's just like that. the comfort levels are unmatched. it's house conditioning not air conditioning. and i think you save energy if the used well water is then used for lawn sprinkling. bob

wetheat1

Thanks

I appreciate all of the input. I was hoping that someone might have some software or a spread sheet to work all of this out. The tube spacing and flow are set by the radiant heating so I want to figure out the potential cooling capability based on that. There will be an air system to handle dehumidifacation, make up air and to provide whatever cooling the floor can not.

RB_2

Performance

adopted from my previous post...at 79 deg f room temp between 60 and 70% rh, surface dew point should be between 64 deg f and 68 deg f.

At 66 deg f floor surface temperatures 10% occupants would not be happy or 90% would be happy…anything cooler and occupant discomfort will go up.

With a 66 deg f low limit floor temp & 79 deg f high limit room temp the output on floor cooling is appx. 16 btu/sf sensible cooling based on a 1.29 cooling coefficient. ( Can be boosted with ceiling fans)

Assuming a floor resistance of R1.4 above the tubes, negligible absorption from ground below slab, 12 inches on center, fluid temperature would have to be a nominal 44 deg f which is why radiant floor cooling systems in this scenario design for a narrower delta t of 10 deg f instead of 20.

A 10,000 sf slab at 16 btu/sf, 10 deg f delta t, 50/50 glycol is a nominal 35 US gpm.

Divide 35 by the number of loops and you’ll have your flow rate per loop.

Enter the PEX manufactures pressure loss chart and find the flow rate per loop and cross-reference the head loss at your installed length…ensure the installed circulator can deliver the performance.

In summary if you have a source of water capable of discharging into the slab at 39 deg f, and holding a 10 deg f delta t you can absorb up to 16 btu/sf of sensible heat provided your circulator can over come the differential pressure at the design flow per loop.

Any other sensible and latent loads beyond the 16 btu/sf will require cooling through other methods such as the ventilation system.

I have attached an illustration of a typical hybrid system.

You can contact me at 403.236.9560 to discuss specific control strategies.

rb

RB_2

Here is a sample...

paragraph from the report

ASHRAE Transaction Ref # DA-00-8-3
Using Radiant Cooled Floors to Condition Large Spaces
and Maintain Comfort Conditions
Peter Simmonds, Ph.D. Stefan Holst, Member ASHRAE
Stephanie Reuss Wayne Gaw Associate Member ASHRAE





"Many papers have been written on improved comfort
conditions using radiant systems for both heating and cooling.(Olesen 1997; Simmonds 1993, 1994). Large areas have
previously been conditioned using radiant systems, but a
200,000 m2 radiant cooled floor of the 500,00 m2 International Airport in Bangkok proved quite a challenge. Traditionally, airports are conditioned by ventilation systems that vary either flow or temperature or both to the space. Simmonds (1996a, 1996b) described the design process for the displacement ventilation system proposed for this airport. Holst et al. (1998a, 1998b) described the advantages of using a radiant cooled floor together with a variable-volume displacement system. This report also showed how the envelope design was optimized to reduce the heat guide to the space and reduce energy consumption.

BUILDING CONFIGURATION
The main terminal building is rectangular in shape and is
constructed from single clear glazing and PTFE materials. The roof of the terminal and parts of the concourses are shaded, or partly shaded, by solar shading devices and roof overhangs. However, a majority of the concourses have no external shading devices. The PTFE material does provide a sufficient barrier for direct solar, but the single clear glazing offers very little resistance.
The thermal resistance of both PTFE and single glazing is
relatively low, and the conductive heat gain to the space would be quite high if traditional indoor temperatures of 24°C were to be maintained. During April, the warmest month, ambient temperatures vary from 34°C to 36°C and there would be a 10°C to 12°C temperature difference across the envelope. A variable-volume displacement system was designed to maintain the required temperature in the occupied zone (24°C). Stratification would be enhanced by this system so that temperatures on the inside of the building envelope would be nearly equal to the ambient conditions, virtually eliminating the convective heat gain to the space. The design and evaluation of the variable-volume displacement system have been discussed by Simmonds (1996a, 1996b)....

The entire report is very interesting and practical.

Full report can be purchased on-line at www.ashrae.com

RB

don_9

Mr bean

> adopted from my previous post...at 79 deg f room

> temp between 60 and 70% rh, surface dew point

> should be between 64 deg f and 68 deg f.

>

> At

> 66 deg f floor surface temperatures 10% occupants

> would not be happy or 90% would be happy…anything

> cooler and occupant discomfort will go up.

> With a 66 deg f low limit floor temp & 79 deg f

> high limit room temp the output on floor cooling

> is appx. 16 btu/sf sensible cooling based on a

> 1.29 cooling coefficient. ( Can be boosted with

> ceiling fans)

>

> Assuming a floor resistance of

> R1.4 above the tubes, negligible absorption from

> ground below slab, 12 inches on center, fluid

> temperature would have to be a nominal 44 deg f

> which is why radiant floor cooling systems in

> this scenario design for a narrower delta t of 10

> deg f instead of 20.

>

> A 10,000 sf slab at 16

> btu/sf, 10 deg f delta t, 50/50 glycol is a

> nominal 35 US gpm.

>

> Divide 35 by the number of

> loops and you’ll have your flow rate per

> loop.

>

> Enter the PEX manufactures pressure loss

> chart and find the flow rate per loop and

> cross-reference the head loss at your installed

> length…ensure the installed circulator can

> deliver the performance.

>

> In summary if you

> have a source of water capable of discharging

> into the slab at 39 deg f, and holding a 10 deg f

> delta t you can absorb up to 16 btu/sf of

> sensible heat provided your circulator can over

> come the differential pressure at the design flow

> per loop.

>

> Any other sensible and latent loads

> beyond the 16 btu/sf will require cooling through

> other methods such as the ventilation

> system.

>

> I have attached an illustration of a

> typical hybrid system.

>

> You can contact me at

> 403.236.9560 to discuss specific control

> strategies.

>

> rb

RB_2

Wire to Water...

This article can be downloaded from ASHRAE

Wire-to-Water Efficiency of Pumping Systems
AUTHOR(S): James B. (Burt) Rishel, P.E.
CITATION: ASHRAE Journal, vol. 43, no. 4, p. 40, 42, 44-46
KEYWORDS: April 2001, Pumps
YEAR: 2001

ABSTRACT:
In the past, wire-to-water efficiency of pumping systems was seldom considered except for very large pumps where the wire-to-water efficiency of the pump-motor combination was of significant importance.Thead-vent of higher electrical costs inconjunction with the emergence of the variable speed drive and digital electronics has made wire-to-water efficiency invaluable for smaller pumping systems.

Trust all is well with you and yours and look forward to seeing you soon.

RB

don_9

I am sorry

But I don't see it,I can under stand the vav or cav system
reheat,economizer,all important issue in dealing with IAQ.
But you already have your chill water,Be you used it at the airhandler why do you have to add infloor?
Do really need Two system to get to the same outcome
All I can say is I would love to learn the sales technique
from the guy who sold that system,Other then saving space with infloor,I don't see it,Where the savings?Lots of extra expense with infloor,Obvious the sky was the limit on this job.

RB_2

On the contrary....

...the sky was the limit so to speak.

What would the savings be to cool sensibly with water compared to air in terms of horsepower and plant efficiencies?

Suppose for a moment that 50% or more of the cooling load was sensible and could be handled by a radiant cooled floor or chilled ceiling reducing the volume of air to ventilation and latent cooling...what impact would this have on blower horsepower?

A heating comparison would ask...what if the ventilation load was separated from the heating load...and the heating was handled by radiant. The air handling system becomes considerably smaller, with all the associated benifits from smaller ducts, smaller blowers and motors, less duct losses etc...

If we ask what happens to the effciencies of a condensing boiler with low temperatures and flip it around and ask what happens to the effciencies of a chiller plant running at a higher fluid temperature...do we get simlar answers?

What impact would a 50% or more reduction in air volumes have in duct sizing, material,installation and construction costs...parasitic gains etc...?

Operating cost are a major consideration in such large projects and radiant cooling, particulairly radiant chilled ceilings is one of the recognized methods of reducing operating costs.

There are numerous reports and studies showing the benifits of radiant cooling...one the most recent is a just released U.S. Department of Energy publication:

Energy Consumption Characteristics of Commercial Building VAC Systems,
Volume III: Energy Savings Potential Prepared by
Kurt W. Roth, Detlef Westphalen, John Dieckmann, Sephir D. Hamilton, William Goetzler, TIAX LLC, 20 Acorn Park, Cambridge, MA 02140-2390

I'd be happy to post a list of other independant reports and where they can be accessed, if requested.

As a side note...one of the neat things about the senior engineer on the airport project...Dr. Simmonds long before he became an engineer, was a pipe fitter and put himself through University at night...guy has no tolerance for salespeople or academics with no real world experiances...which is why he ends up on these projects doing stuff others can't do.

..tommorow when I get back to the office I'll post the energy savings comparison from the report.

Keep posting and challenging these topics...

RB

don_9

the debate

Ok I have no problem with the ceiling panel ,Yes I understand the greater the surface area the hot air comes in contact with the better the chance for the heat to be
absorb.Far better then trying to push the air back to a
central return,but once the air become cool it density increases and become stagnet,Now you have to depend
on a fan to get it moving toward the ceiling anyway.I also
understand the goal for high shr,efficeny it pound in one head constanty by ari rating.But high efficency and comfort is two different things.What about the latent load? specific humidity is a big problem with comfort level,not
to mention controlling humidity to lower level to control mold issue.So we have radiant cooling to handle a certain amount of senible,then one need to depend on another system to control the latent issue and the iaq issue,Now add some
reheat,steam humidifider, hrv and lots of control to handle the condensate issue."Indoor rain"
Where's the payback verse the time it will take to see any.
Mr Bean I am not trying to say that this system will not work,Its already been proven it can,I see it has a hard sale in out of reach for most and only accessible to those
with deep pockets.

Dave Yates (PAH)

thanks

It is refreshing to have sharp minds such as yours and Siggy's to help us wade through the mysteries and hype surrounding radiant cooling. Unlike some who simply claim it can work and provide "free" a/c, you and others are researching and providing substance. Your (collective) hard work is appreciated.

Thanks,

Dave

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RB_2

Energy savings for the airport project

as promised....attached savings graphs

Note the power consumption to cool the sensible load with radiant vs air.

RB_2

Dave...you're not saying we have pointed heads ...

and wear rubber waders for a living are ya? Cause if you are I'll ask you to start doing those female impersonations again!

rb

Dave Yates (PAH)

someday

I want to meet your better half and give her my sympathies! Female impersonations? I deny everything(G).

Free floor A/C for everyone - just run all of that fresh potable water through a mile or two of 3/8 or 1/2 inch PEX and you too can enjoy the benefits. Wanna buy a bridge with that? PS - booster pumps for point of use water flow not included.

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Mike Kraft

DAMN BEAN!!!

You're freakn' hot n cold..........love your raps:)

cheese

don_9

pie chart

Mr Bean, or we comparing chill water with fan -virus chill
water with radiant,or dxsystem with no chillwater virus
chill water radiant panel? I see no fluid on the original concept.Thanks for all your help.

RB_2

Looked over the report...

and no specific details on the original concept...lots on the optimized concept. Have seen Berkley University comparison reports with chilled water on fan/coils vs chilled water on radiant...you s/b able to download them off the net...

email your address to me and I'll send what I can on this topic without infringing on ASHRAE copyrights. The noted report above from the D.O.E. is public domain but they haven't posted the latest version...I'd be happy to send this to you as well.

Best regards,

RB

....Mike and Dave, my wife says she noticed a change when I started hangin' with you guys and my Mom always said be careful who you play with.....go figure.