radiant heating/cooling for art museum

Jeff Lawrence_25

Did a case study about a radiant heatng and cooling project in Chattanooga.

“We are controlling the radiant cooling aspect of
the floor by maintaining the floor at five degrees
above the outside air dew point,” says McKenzie. “This
prevents condensation on the floor while providing radiant
cooling and immediate absorption of heat due to direct sunlight.”

Good luck.

Tessa

radiant cooling/heating for art museum

I'm an architecture student and I am designing an art museum in the adirondack region of NY. I wanted to use radiant heating through the floors , but would rather not have a separate system for cooling. I've heard that radiant cooling causes a lot of problems because of condensation and was wondering what I could do to prevent this. In my building, I am planning to have clerestories, so if there is a way I could ventilate the building as well as cool through those, it would be great. What other options do I have for ventilation systems that are non-obstrusive to exhibition space? Also, if I decided to use radiant coils for cooling as well, how would I make use of a dehumidifier? Thank you!

GMcD

You \"heard wrong\"

I assume you've done a google search on "radiant cooling" and read the literature and reviewed the laws of physics for yourself. That being said, why the floor? Radiant surfaces can also be the walls, and ceilings. Radiant cooling from the floor can be done, but it's not the best way for effective radiant cooling, due to the masking of the floor by furniture, other floor coverings, and the radiant emitter location relative to the human body. Overhead radiant heating and cooling provides the best emitter area relative to the humans.

First of all a Museum will need some pretty good control of humidity and air temperature so the display materials are not stressed. Most Museums like the interior conditions kept as steady as possible, with a temperature variation of not more than 1F or 2F over a 4 hour period, and a relative humidity level of around 45% +/- 5% over 4 hours. So, if the ambient air conditions are being kept at 72F and 45% RH, the ambient dewpoint will be around 50F. So, if the floor (or better, the ceiling) was to be used for radaint cooling with a nominal surface temperature of 64F, there is no danger of any condensation.

BUT: since the ambient conditions want to be held fairly steady, there will be a requirement for a prety good air system to maintain those conditions, and the radiant system would not be providing that much more sensible heating/cooling at the end of the day, and may be a premium that is not needed.

There ARE museums in Europe that use radiant heating and cooling and a heat recovery ventilation system to maintain these stringent indoor conditions, BUT, they rely on very high performance envelopes to reduce the heating and cooling loads down to the bare minimum thermal variations so the radiant system can maintain the steady state room conditions while the ventilation system is reduced to doing just latent load (de-humidification, and added humidity control).

The proper Museum "systems design" starts with the envelope to allow a steady state interior condition, which can be maintained by a hydronic radiant system, and a smaller air system. If the building has high variations in thermal loads, radiant won't be as effective a solution for low energy and comfort. With Museums and Art Galleries, the "contents" demand higher HVAC Conditions standards compared to the occupants.

Tessa

reason

The reason for the coils in the floor is to keep things off the ceiling because of the clerestorie design. I also didn't want radiant heating in the walls because that is prime area for artwork. I realize that the room does need to be kept very stable (to reduce condensation) and was wondering what sort of air circulation/ventilation system would be best to do this. The heat recovery ventilation system you mentioned is common right? Thanks so much for the speedy reply!

Mike T., Swampeast MO

The key to radiant cooling is dewpoint. Unless your radiant collector (in the case of cooling) is designed to collect and drain condensed water, you MUST keep the dewpoint of the air surrounding the radiant panel a comfortable margin below that of the panel. Say your radiant collector is at 70F--you want the dewpoint of the air comfortably below--say 65F.

Clerstories and "roof windows" are certainly great for art museums. Design them nicely and you'll get great natural light with little need for artificial and much of the artwork will look its best--don't forget that artists LOVE the diffuse light from the North and their work is often produced under such lighting!

If those clestories are active you can design for nice, natural ventilation when the outdoor conditions are favorable. Of course when they open you also need active (fan-assisted) fresh air input. How much fresh air depends on how many people are in the museum. A simple human-operated control labeled with a scale that begins "empty" and ends with "full" AND a competent operator will likely exceed the capabilities of computer control at MUCH less cost and complexity.

This will work for fair weather with fair occupancy. Let it get hot (or worse hot AND humid) or have a high occupancy and you need more complicated treatment of incoming air. That air MUST be dehumidified and/or "tempered" to GUARANTEE that NO CONDENSATION occurs on your radiant collector. In other words you install cooling coils into the fresh air ventilation stream. Such "cooling" coil will vary from just reducing the humidity of the incoming air to actual cooling.

Condenser unloading--either staged or proportional (www.rawal.com)--will work WONDERS to give you the proper dewpoint of the incoming air.

Depending on the climate and the weather at the time there will likely be times when you must also recirculate AND cool indoor air to maintain the proper dewpoint. This involves proportional control of air dampers and variable speed blowers that vary both the volume of air moving and the proportion of fresh to recirculated air.

You'll find good information on how to do ALL of this in books (old AND new) and from the web.

I assert that your goal is to STILL have the system controlled by a simple "empty-to-full" dial.

Heating is similar and will require all of these components but at least you don't have to worry about dewpoint.

Weezbo

We have a sayin here It pays to wander off the Wall.....

before you go too much further, take a hyke to the local library and then off to Archives and the Viewing room.... check on some of the minor technicalities involved in space conditioning in those areas.... i cannot see playing with only 1/2 a deck ,unless it is Penny Pack(an Eskimo card game that doesn't require a full deck)

there are quite a few distinctions that may need to be made in a museum......

Brad White_9

As an HVAC engineer

with experience in museum, archive and rare collections design, I can tell you that the advice you have received thus far is as good as it gets (short of a design of course).

The issues of dewpoint control? May I take that a step further?

Think of the air mass you are trying to dry out as a sponge.

That the two principal ways to dehumidify is to cool the air below the dewpoint (wringing out the sponge) or use of a dessicant wheel (absorbing the sponge with a bigger, thirstier one), which then has to be recharged by drying *it*. Both incur energy penalties. Either one works but dessicants are generally reserved for where the humidity has to be much lower than cooling can economically achieve. So cooling is the first choice because it is also conventional and can assist the cooling of the space in addition to moisture control.

The other principle in museum, library and rare collections design is that the "collections are the occupants". This is essentially what Geoff McDonell had pointed out, among his uniformly excellent advice.


People are secondary and transient visitors. Ventilation is provided for them and to absorb/dilute any outgassing from the collections.

Assuming that much your sensible cooling (that which is temperature and not humidity-related) can be met by radiant cooling, chilled beams and such, then your air-side latent loads have to be scrupulously catalogued.

This would mean people in the space plus the outside air needed to be conditioned to support them. (You would not count humidifiers because, of course, they work at the low end of the range. You want to dehumidify from the high end of the range.)

So the best vehicle in a radiant-cooled structure is (de-facto and IMHO The Ventilation (Outside) Air.

Normally, this is 20 cfm per person but in areas of high occupancy especially if sporadic, it may be reduced to 15 cfm per person.

Here is the fun part (OK, fun for engineers...). The sensible load of a person is about 315 BTU's per person per hour at a standing/light work/walking level of metabolism. The latent load from a person is roughly the same, at 325 BTU's per person per hour.

These have all been adjusted for diversity, the number of adults versus children, women versus men, and generally runs about 85% of these numbers on average.

The latent load is the equivalent about 1/3rd of a lb. of moisture.

To remove this amount of moisture, (each person "owns" 20 cfm of outside air, remember) that air would have to be cooled to the low 40's F, at least 42 degrees if not lower. That costs a lot and may take two stages of cooling.

So what we routinely might do is to *double* the total airflow and keep the 20 cfm constant. Each person gets 40 cfm total airflow of which 20 is outside air, as a minimum.

This air can be cooled to more conventional temperatures, with a 52 degree dewpoint.

Further, CO2 monitoring can pick up on high occupancy or better yet, low occupancy and reduce the OA load and associated energy expense.

That is the short-hand lesson for today


Best,

Brad

Tessa

thanks everyone

Thanks to everyone! I've have been researching since I've asked this question, and all the advice and knowledge you've given is very very helpful. Thanks again!

Paul Pollets

Heeding Good Advice

Tessa, Geoff is one of the very few engineers in N. America specializng in both radiant heating/cooling. I'd advise you to carefully consider reviewing the mechanical design with an ME who has this experience.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"