Hydronics – Warming up wide open closed spaces

Hydronics – Once again we are well into our Canadian heating season and faced with the challenge of keeping our work spaces warm and comfortable for the people and equipment in those areas.

For homes and offices, the doors leading into these spaces are not kept open very long on a cold winters day, and often even have a double door arrangement to minimize heat loss. But what about larger commercial buildings like airplane hangars, garages, maintenance facilities or ambulance and fire station bays?

These facilities all have large doors that require frequent openings and closings, and very often the pieces of equipment coming back into those spaces are cold and covered in snow and ice.

For commercial facilities, a significant amount of energy is required to simply warm those vehicles back up, not to mention keeping the work space warm. Service vehicles like ambulances, police cars and fire trucks are always on standby, so having those vehicles and their equipment warm and ready to go on a moment’s notice is crucial.

Pulling a large plane or snow plow back into a hangar or maintenance garage would have a similar effect as dropping an ice cube in a glass of water. It would contribute to cooling that space if supplemental heat was not used to keep the space warm.

Radiant heating applications are an excellent way to heat large garage spaces during our cold Canadian winters. Such facilities often have thick concrete slabs ranging from six to 12 inches in depth that make great radiators for keeping these facilities comfortable.

In commercial garages/bays/hangars radiant tubing installations would typically be located in the bottom half of the overall tube thickness. For example, in a commercial airplane hangar with a 10” thick slab, the tubing would likely be located about 6” deep.

Having the tubing located in the traditional 2” depth would provide a faster response time, but with heavy loads from the commercial equipment, the structural integrity of the slab could be compromised if the tubing was located too close to the surface.

Another advantage of keeping the radiant tube deep in the bottom portion of the concrete slab is to reduce the possibility of puncturing the tubes when anchor bolts are installed in the slab for mounting shelving/racking and other pieces of facility equipment.

When using radiant heating in thick concrete slabs, care must be taken to minimize over-heating or under-heating the slab, especially during the shoulder seasons of the spring and fall when heating requirements fluctuate frequently.

Thick slabs do take a long time to warm up when first started and also take a long time to cool down due to the thermal inertia of the slab. Proper control of the slab will help minimize this effect, however radiant heating is quite “self-regulating.”

Working the slab

When installing radiant tubes in thick slabs:

1. There is approximately a 4ºF to 6ºF increase in hydronic water temperature needed to produce the same surface heating flux for each inch deeper than 2” that the tube is installed.

2. The deeper the tubes, the greater the mass heated, and therefore the more thermal inertia to control. Controls have to compensate for the slow responses from the slab.

3. For thicker slabs with deeper tubes, each inch of concrete causes an approximate two hour lag in temperature fluctuation control. Pick-up time is reduced for deeper tubing with higher water temperature from the heating plant.

4. If you want a faster pick-up time from a thick slab, it will require an oversized boiler to provide the energy to heat the increased thermal mass.

Losing warm air

Many garages, service bays and airplane hangars use forced air heating systems or hydronic fan coils to heat the given space. Gas-fired radiant tube heaters are also quite common. If it takes 30 minutes to open the doors, bring in a plane and then close the doors, all of the heated air in the space will escape while the doors are open. The system would have to reheat that space, and it would be a considerable amount of time to get the space comfortable for the workers.

Floor-based radiant heating systems would experience a minor drop in temperature during the aircraft loading process, and the radiant slab would increase its output once the air got cold. The technicians working in that space may see their breath due to the cold air, but the radiant effects of the slab would be providing heat to them and the aircraft, and would keep everyone comfortable.

A self-regulating system

If a radiantly heated garage starts to overheat slightly because the outside temperature rises, the room air temperature becomes closer in value to the slab temperature, thus decreasing the temperature difference between the room and the floor surface. This, in turn, reduces the heat output of the radiant floor. The result is a self-regulating effect. The more the overheating, the less the slab releases heat to the room.

The opposite is also true. If the space gets colder due to heat losses, such as an opened garage or warehouse door, the delta T between the air temperature and the floor temperature becomes greater, and the slab then releases more heat to the room.

A high-radiant-output slab, like a commercial garage or hangar, would have less of a performance drop or increase from a 2°F room temperature change than a slab that was only supplying minimal radiant heating.

Warm, under the vehicle

Another advantage of a floor-based system is the effect of the warm floor for technicians who are under vehicles to service them. What better place to have your heat source than right next to where you are working?

Radiant floor systems are also great for quickly warming up the underside of vehicles and melting any snow and ice buildup that has been established while those vehicles were out on the road.

I’ve talked to technicians who work in establishments with radiant floors and they love being able to pull a snow-covered vehicle into a bay at the end of their shift and arrive the next morning to work on a warm, dry vehicle that is not sitting in a pool of slush and water.

By Jerry Leyte

Jerry Leyte, P.Eng., MASc., is the sales manager for Central Canada at Uponor. He can be reached at [email protected]