Volume 26, number 2, September 2012

Ceiling space heating: A feasible and comfortable solution

In the wake of new approaches to space heating using ceiling-mounted diffusers, Gaz Métro wanted to know if those approaches would work without peripheral heating, particularly in office or multi-tenant buildings. In giving a mandate to the Natural Gas Technologies Centre (NGTC), Gaz Métro wanted to demonstrate the potential of a ceiling-mounted space heating system1 without any peripheral heating.

Is it possible to warm a room from the ceiling while maintaining the comfort of the occupants without peripheral heating? What are the important criteria to be taken into consideration in the design? These questions were central to the tests conducted by the NGTC.

The NGTC has a test room (see Figure 1) so it can carry out the simulations required for this type of evaluation under controlled conditions.

Figure 1: NGTC test room

The test room is a reproduction of a 3.4 m x 5.5 m x 2.4 m room that could be in either a residential or a commercial building. The ceiling, floor and three of the walls are adjacent to a heated room. Just one wall, with a window, is exposed to outdoor conditions.

In order to reproduce the outdoor temperatures under which the tests are to be carried out, a sealed enclosure is fixed against the window wall. This completely sealed enclosure is linked to a conditioning chamber by ventilation ducts. This set-up ensures a completely temperature- and humidity-controlled environment.

In order to evaluate the diffusion of temperatures in the room, the comfort (according to ASHRAE Standard 55-2010) and energy needs associated with different heating systems and the distribution of air from the ceiling, the following measure­ments were taken: air temperature, air speed, noise in the room, and air flows at the diffuser outlets.

Measurements were taken for three types of installation: two models of ceiling-mounted air diffusers, one with a vertical projection outlet, one with a horizontal projection outlet, as well as electric baseboard heating. The vertical and horizontal projection diffusers are shown in Figure 2.

Figure 2: Round diffusers with horizontal projection (left) and vertical projection (right)

The three systems were evaluated by modulating several variables: control over the room temperature, insulation levels and outdoor temperatures. Different operating parameters were also simulated: temperatures, flows, diffuser positioning.

The results of the tests carried out at the NGTC showed that a well-thought-out warm air ceiling distribution system heated a room sufficiently, while ensuring the comfort of the occupants. However, what is important in the design is that the air diffusers are well positioned and supplied at the right speed and the right temperature.

The NGTC study found that, of the three types of heating tested, the warm air vertical projection system showed the least temperature stratification between the ceiling and the floor (see Figure 3).

Figure 3: Typical temperature distribution profiles

In conclusion, it was found that a well-designed heating system using ceiling-mounted air diffusers can offer increased comfort to the occupants. Also, a central warm air heating system, as opposed to peripheral heating, facilitates the introduction of energy efficiency measures such as heat recovery from other parts of the building, while freeing up space around the room’s perimeter. The encouraging results of this first NGTC study on the subject opens the door to other analyses, such as conducting an on-site demonstration, producing a good practices guide, etc.

Marc Beauchemin, Eng., CEM

1 NGTC studies: Warm air versus electric baseboard heating, Project No. 329407. Analysis of experimental results by Geneviève Bussières, Eng., CMVP