Heat loads

Unknown

Thanks Mike,

How do I determine the EDR of an air handler steam heating coil?

Unknown

Heat loads

I realize that a proper block heating load calculation is the best way to size a steam (or any) boiler. However, I would like to ballpark the required heating input of a steam boiler for a commercial building. Is there a rough btu/hr/sq ft factor that I should apply? The building is an a relatively mild climate where the winter design temperature is approximately 20 degrees F.

I have been told that 3 to 4 btu/hr /sq ft would cover it, however, this sounds way too low to me.

I would appreciate any assistance.

Mike T., Swampeast MO

Steam boilers are sized by the amount of connected radiation (in square feet of EDR).

Hot water boilers are sized for the heat loss of the structure.

"Rules of thumb" are guesses that have no place when it comes to sizing a boiler.

Christian Egli

The wild operational range of steam fed air handlers

Condensing steam like there is no end to it.

The colder it gets, the more steam gets sucked into the gadget all the while the hot blast of air streaming towards you remains just as hot. Within reason, steam usage modulates from nothing to infinity. It all happens with no complicated valves, only a drop in pressure which the boilers detects and compensates by firing off. A marvel.

Hot water heat does not have that much agility. Hot is hot and the colder the air is at the inlet, that much the colder your outlet air will be. You can fiddle with the valve of course, but you’re still limited by the temperature and the quantity of water you can flow through the air heater. Then, you’ve got to fiddle with supply water temperature.

But with steam, you probably can feed as much steam as you want into your air handler. To figure out how much it will actually devour, you need to look at the thing the way you would look at a furnace and the room it heats.

Ball park figures are only crude estimates of what you’ll need. A better thing to do is a full calculation. With commercial buildings it is even harder to get good figures because of the way the space might be used.

I would build the system thinking small at first, but with the ability to add boilers to the system. Adding boilers is straight forward. The owner should easily understand the strategy, and you might not get burned.

Several small boilers will give flexibility. For instance, one small and one larger boiler will give you three operating levels, like a three way light bulb.

Here, with about 0 deg F as design temperature, many buildings I’ve had the opportunity to look at are powered with 3 to 7 BTU/hr per cubic foot of volume. These are commercial / industrial buildings. My home falls within the same range.

To do back-of-the-napkin calculations while having a beer, I generally use 4 BTU/hr per cubic foot of heated volume. By magic it corresponds very nearly to metric units of 40 watt per cubic meter. I can do math even after two drinks.

Your design temperature is the likes of those in North Carolina, where it is much warmer than here. Your numbers should be lower.

Moreover

The fans on your air units, are they each individually controlled by a thermostat or are they all on all the time? If all on all the time, be worried of under sizing, you might never get heat to the distant parts of the building.

If you’re lucky enough to have a vacuum pump in your system, think of restoring it too, it will greatly help distribution and make the start up time instantaneous.

Lastly, check, test, fix, replace all the traps. This is most important. If you’re installing new ones, add the extra test valves, it is worth it. A bad trap will stop the system stone cold and hurt your ears.

Best regards.