Unit Heater: Hot Water in Steam Coil?

[sadele89]

Could a unit heater designed for steam be used for hot-water applications? I cannot find a hot-water unit heater that will meet project specs for max entering water temp. There are steam units for which the coil will meet those temps, but there is no steam service on this project.

 

[EnergyProfessional]

Probably yes. But you don't get manufacturer performance data. i assume performance will be reduced due to lower temperature.

 

[Compositepro]

You can use a steam coil but performance will be greatly reduced from the steam rating. There may also be subtle mechanical design differences that introduce process problems.

 

[chicopee]

If you stated the type and the manufacturer of the unit heater, perhaps someone may have additional information. I would also suggest that you research Mark's and Kent(Power) mechanical engineering handbooks as these handbooks have a lot of information on hot water heating systems that include heaters.

 

[GT-EGR]

Your capacity will be greatly reduced without the latent capacity of the steam exchanged in the coil

You’ll need to get a much larger coil/unit heater nominal heat - and compare the coil size, rows, fins, airflow, etc with some other similar coil that is similar but rated for hot water. It’s odd though that a unit heater manufacturer doesn’t have data/a hot water rated option for their equipment.

 

[quark]

The impact with respect to latent heat of steam and sensible heat of hot water will not be that huge. If we consider that the system was running at 3.5barg steam, with a delta T of hot water at 10C, per unit mass of water, the heat content is 50 times less. Nevertheless, volumetric flow rate with water will be more to offset that.

 

[GT-EGR]

For reference, here’s a link to a unit heater catalogue that shows performance ratings of the same equipment using steam or hot water.

So depending on the size it’s maybe about a 25% drop in capacity. So maybe not as huge as my first post referenced. This is 200 deg F (high for a normal heating hot water system) water vs 2 psi steam.

http://mesteksa.com/fileuploads/Literature/Vulcan Radiator/VVSD-6.pdf