Infrared Heating

TeachMeSteam

Anyone on this forum have experience with infrared heating? Please let me know because I have some very specific detailed questions about them and I hope to have an interesting conversation about it.

I know electricity is one of the inefficient forms of energy transferrance. That converting natural gas or coal into electricity which then travels along electrical lines to far reaches of the land, it creates a huge amount of waste. And thus infrared heating which relies on such power becomes very inefficient.

But what about infrared heating that relies on gas power?

Or, can other efficiencies be made that make it better than HVAC's?

Please respond to this thread or private message me if you're more shy. I am planning some major renovations to heating/cooling systems and I am looking for input on people who know what they are talking about.

Thanks.

Jamie Hall

Gas fired infrared heaters are used in agricultural applications -- actually, rather commonly. These are high bay applications in barns, mostly. It works well at keeping the critters reasonably warm; it doesn't do a thing for, for instance, the water (immersion heaters) or feed (in the bigger dairy applications, that's done in warm milking parlours, for instance). The units have to be vented, which isn't a problem in a barn but could be in other types of structures.

Solid_Fuel_Man

I've installed some in an airplane hanger. About the simplest thing I've ever seen for the money.

Forced draught bunsen burner and simple control on one end and a vent on the other. Don't believe they are very efficient as far as heat transfer. The stack temps were quite high as far as I recall. Basically just a burner in a long U bent tube.

I'd prefer radiant slab in most applications.

delta T

The biggest problem I see with the gas infrared heaters is that the temperature of the tube must be very high, which makes them inefficient. The advantage is that they still work reasonably well in a structure that has an extreme air exchange as they are not heating the air at all. They heat objects (floor, tool bench, people etc...). I see a lot of automotive shops use them because the bay doors are open all the time, airplane hangers as Solid_Fuel_Man said, and barns as Jaime said are also good applications for the same reason. I don't think there is really a huge appeal as far as efficiency goes.

Here is the dilemma. For a given amount of heat to transfer to through direct radiation (infrared) the two values that matter the most are the delta T (difference between the temperature of the heat emitter and the object/s being heated) and the surface area of the emitter. These two values are proportional. If you use a radiant slab, (which is an infrared heater in another form) you have a lot of surface area, and therefor your temperature can be low. If you use a gas fired radiant tube heater (the kind you see in shops, barns and aircraft hangers) you have much less surface area, and so you need a much higher temperature to achieve the same heat transfer. The highest real efficiency you are going to get is most likely a low temperature, gas fired modulating condensing boiler feeding a radiant slab. Or if you look to the electric side, a water source or ground source heat pump supplying the same radiant slab would be the best choice for efficiency. However either of these systems would work poorly in an open garage as it doesn't really 'feel' warm (or to make is so would necessitate temperatures too high to walk on), whereas an overhead radiant tube heater will 'feel' like standing in the sun on a warm day, thus keeping the occupants happy (ish).

It all depends on the application, which you have not told us yet....

What specific questions do you have for us?

hot_rod

This paper has a footnote that mentions a study done comparing infrared to other types of heat.

http://www.ahrinet.org/App_Content/ahri/files/Product Section/INFRARED BROsinglePGS.pdf

The amount of energy input to heat output would be one efficiency. Another would be to determine the amount of that energy conversion that gets to the load. Fuel efficiency and also distribution efficiency.

80- 85% seems to be a efficiency number I see in manufacturers specs.

Being energy transfer by radiation it would be considered a line of sight energy transfer.

Tinman

I think they are a great fit for many applications that the manufacturer's will certainly outline. I had one in my shop 25 years ago over a sheet metal layout bench. I kept the thermostat for the hanging forced air unit heater at 45* F and then would manually use the infrared while I was working at the bench. I have friends who use them on their patios for shoulder seasons and cool evenings.

TeachMeSteam

We all know that forced hot air is a poor method of heat transfer. The only thing going for it is the easy installation. However, you're trying heat air which in itself is an insulator. Other negatives is that it dries out the air. If you try to humidify the air with humidifiers, you start getting into complications with mold. Additionally, since air is an insulator. The transfer of heat from the air to the chairs, ground, desk, carpets, etc., take a very slow time. Even though the HVAC might cycle off as the "air" heats up, the objects themselves haven't heated up yet. It takes a while.

Moreover, heat loads aren't calculated very accurately and we frequently get fast hot, then fast cold cycles which aren't very comfortable.

I wondering what the best heating systems would be considering all the new technology that is currently coming out.

EBEBRATT-Ed

As others have said it depends on the application. Gas fired infrared excels on loading docks, garages, warehouses etc. It heats the slab in high heat loss applications so that when garage doors or loading dock doors are opened in 0 deg weather the heat instantly leaves the building. (heat travels from hot to cold) Because the slab is a huge heat sink as soon as the doors are closed the air is heated quickly from the slab

hot_rod

Three modes of heat transfer are conduction, convection and thermal radiation. One or a combination of these modes are used in various types of systems.

62% of of heat released from a human body is via radiation. To me an ideal system for comfort involves radiant surfaces. I'd suggest a low temperature supply radiant panel would be one of the best, choose you heat source based on your fuel cost. If electricity is the fuel, a heat pump supplying low SWT would be an efficient system.

But an ideal comfort system should also include humidity control, air exchange and filtration. So it may require a few different systems to provide ideal.

As with most things the "best" heating system is in the eye of the beholder. Nice that we have so many choices.

ratio

The inestimable Mr. Holohan mentions the Cold 70, same thing. Note that radiant heat does not decrease linearly with distance, meaning you'll melt/char/burn stuff that's too close.

What, exactly, are your questions?

jumper

My first guess is that I want as hot as possible short of glowing. That radiant source will warm the walls and floor so that I will feel warm despite cool air temperature. I have had some success with undersized radiant electric heaters at ceiling level. Since they're undersized they stay on most of the time and the living space is comfortable without being too warm.

hot_rod

I have sat outside dining in Chicago mid January under radiant heaters. They can make the top of you head sizzle, but legs and feet under the table don't "see" or feel the radiant heat.