RADIANT  VERSUS  CONVECTION

A gentleman I once worked for had the reputation of being an expert with respect to electric resistance heat.  His name was Larry Morgan.  We would discuss electric heating applications for hours on end.

One of our discussions led to the question of “What is the perfect heating system?”  Larry’s response was, “Every square foot of surface in the space, should radiate heat”. That would include the floor, ceiling and walls. Spreading out the heat is the key element to “people comfort”. Radiant ceiling cable offers one of the largest heating surfaces to warm the space and people.

We have been asked to look at, and compare two different types of heating methods, radiant versus convection, for high-rise residential properties. Both involve electricity as the energy source. Radiant has two sub-sections. One is using electric radiant ceiling cable. The other will be using electric radiant panels along the perimeter glass. The second form of heat is electric convection or baseboard.

COMPARISONS OF RADIANT VS CONVECTION

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Electric Radiant Ceiling Cable:

Comes to the job site as a spool of cable with spacer strips. The cable is attached to the ceiling using the spacer strips. For the system to be complete, a plaster covering of about 3/16” to ¼” thick will complete the installation. Most of the ceiling will be a radiant ceiling heater. It has been my experience that the electric radiant ceiling cable was the system of choice for some of the more prestigious projects, albeit smaller. (e.g. Ms. Winfrey’s residence at Watertower, The Field’s residence at North Lake Shore Dr., and the 5601 unit at 800 N. Michigan to name a few.) Depending on the heat loss calculated for the space, the amount of heat supplied is around 10~15 watts per square foot. In most cases radiant ceiling cable would be my choice between the two other systems.

• Cons
• More expensive to install.
• Limits what can penetrate the ceiling after installation.
• Pros
• Less expensive product cost than baseboard and radiant panels.
• No noise.
• Invisible.
• Even heat distribution
• Quicker energy transfer than baseboard.

Electric Radiant Panels:

These come to the job site as a packaged heater. Installation can be in a ceiling grid or in a drywall ceiling. Addresses many of the heating issues that were once perceived as an advantage that only baseboard enjoyed.

Panels, if mounted 9’6” above finished floor or less, are an effective draft barrier and therefore would address condensation issues at the glass. The heaters typically come in a two foot wide configuration that produces 188 watts a linear foot. Custom widths and lengths are available.

• Cons
• Heat can be intense right below the heater.
• Slightly more costly to install than a baseboard system.
•  

• Pros
• No noise.
• Less visible than baseboard.
• Quicker energy transfer than baseboard.
• Addresses perimeter loss more intensely than cable.

Electric Finned Tube Convectors:

These come to the job site as a packaged heater. Installation in a wall-to-wall or stand-alone configuration is the quickest of the three systems. The cost to install is typically lower primarily because of the wire way included in each heater and the initial comfort level the electrical subs have with the product genre’.

I am in no way badmouthing electric baseboard heat when I place it third on my list of what I would install. Electric baseboard is an effective means of heating. Trans Energy is a large supplier of electric finned tube radiation in the Chicago market. It has been our bread and butter for years. I just like convectors a little better in a commercial application than in an upscale residential building. The heaters in a residential application are typically maxed out at 250 watts a linear foot.

• Cons
• Noisy.
• Very visible and takes up floor space.
• Slower to heat the space than radiant.

• Pros
• Addresses perimeter loss more intensely than cable.
• Cheaper to install than radiant ceiling cable.

It is important to remember that too much heat in the space is not the way to go with any of these systems. Too much heat with a typical control method would cause the heating system to cycle. Control is another issue I would like to address. With high-end residential construction it is not as much the heater that is the problem (noise, over/under heating), but rather the control method. Any resistance heat in high-end residential projects should be proportionally controlled. It will typically solve the noise issue with baseboard, and increase tenant comfort whether you have electric baseboard, panels, or the ceiling cable.

Why choose Radiation?

The radiation theorem Q=s A (T1 - T2)4⁴  simply states that

heat transfer in BTU/H (Q) equals emissivity factor (s) times the area in square feet (A)

times the absolute surface temperature differences in degrees Rankin

with both temperatures raised to the fourth power.

 

This is as opposed to the convection theorem, which only raises the surface’s temperature difference to the first power. Simply stated, the radiant energy’s ability to transfer energy is much greater than convection.

Bottom line about radiant ceiling cable is as follows:

1. It makes absolutely no noise.
2. It takes up no floor space.
3. The heater is maintenance free.
4. It is more comfortable than perimeter convection because the heat is spread out.

We, Trans Energy Systems, have prided ourselves in knowing electric heating systems. We know application. We know that for high-rise, high-end residential buildings, the radiant ceiling cable system is the right application.

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