Infra -red heating garage

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Hi Guys,

Any idea how to simulate a infra-red tube heating system for a garage.

thanks

Hector Lamprea, P, Eng. LEED AP. C.E.M PO

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Hi, Hector - I recently did this for a LEED submission and had to do an exceptional calculation. There isn't a method of modeling infrared heating directly in eQUEST. I modeled it as electrical baseboard heat and assigned a sub-meter to report the kWh used by the baseboard system in the space. Once I figured out the energy usage in kWh used by the baseboard, I converted it to natural gas therms and then divided by the average efficiency of the infrared system. I submitted a narrative explaining this, and the LEED reviewer accepted the calculation method. I'm sure there are more accurate (and more time-consuming) methods for modeling it, though.

Stormy Shanks, PE

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Thanks Stormy,

I guess this a good estimate, however I would like to show saving over a furnace system ( Most of the Infra-red pipes manufacturers claim between 30 to 50 % energy saving over a conventional furnace system )

Hector Lampra, P. Eng, LEED AP, CEM

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Your infrared system won't have fan power associated with it while your furnace in the baseline will have fan power. You may also be able to justify a lower space setpoint temperature in the proposed model than in the baseline since you're using radiant heat. It seems like ASHRAE has published something about what space setpoint temperatures should be used when you're designing radiant heating compared to forced air heating? Does anyone else remember that? Maybe it's in ASHRAE 55? Normally, you would have to model setpoint temperatures the same in both models.

Stormy Shanks, PE

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Assuming you are talking gas-fired infrared, you can select "Furnace" BASEBOARD-SOURCE. Efficiency, auxiliary electric (if there is a fan) etc. are input in the Unitary Power tab for the system, so you wouldn't need to document an exceptional calculation method unless you wanted to use the reduced setpoint temperature that Stormy suggests.

Regards,
Bill

[Senior Energy Engineer 28Jun2012]

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Hector,

I don't know if this will help or not.

Many years ago, I had to do the analysis of converting two large high bay vehicle maintenance buildings from steam unit heaters to closed combustion infrared heating. The steam plant was extremely oversized and inefficient as several of the buildings originally served by the plant had been demolished. I used a bin temperature spreadsheet for the analysis in this case.

Since one of the benefits of infrared heating is greatly reduced stratification, we took temperature measurements at floor level, normal thermostat height, and ceiling level using an infrared gun. This was done on a typical "cold" day. Knowing the building height, we used the average temperature of ceiling level and floor level (or was it thermostat height???) as the "space temperature" for envelope loads. We probably ended up understating the roof heat loss due to the higher temperature at ceiling level. For the proposed case, we did reduce the space temperature setpoint as infrared heats people and objects first, and not air, which is why it is possible to maintain a comfortable environment at a lower space temperature. My memory isn't the best, but I think we used 60 deg. as the proposed setpoint based on similar, previous projects.

If you're contemplating closed combustion infrared heating, you'll have some fan power to consider, but it's probably less than the furnaces. The combustion efficiency should be better also.

Mike Busman

Michael R. Busman, CEM

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