Fan coil steam temperature

Pumpguy

We all know from the definition of EDR that cast iron radiators are sized for a 215 degree steam temperature which is steam at 1 psi.

Is there a similar simple rule for other types of steam heated heat exchangers such as large fan coils or steam to water heat exchangers for hydronic heating?

I see all too many steam heating systems operating at too high a pressure and I advise that all they really need is enough pressure at the boiler to overcome system pressure drops so they have 1 psi at the farthest radiator.

I'm wondering if this rule is equally true for systems that also have large fan coils and / or heat exchangers for hydronic heating.

I talked to some fan coil suppliers and manufacturers. Their reply was "it depends on the conditions supplied by the architect"

Thanks for your help.

Dennis Pataki,

Spring Grove, Illinois

Pumpguy

Fan coil steam temperature

We all know from the definition of EDR that cast iron radiators are sized for a 215 degree steam temperature which is steam at 1 psi.

Is there a similar simple rule for other types of steam heated heat exchangers such as large fan coils or steam to water heat exchangers for hydronic heating?

I see all too many steam heating systems operating at too high a pressure and I advise that all they really need is enough pressure at the boiler to overcome system pressure drops so they have 1 psi at the farthest radiator.

I'm wondering if this rule is equally true for systems that also have large fan coils and / or heat exchangers for hydronic heating.

I talked to some fan coil suppliers and manufacturers. Their reply was "it depends on the conditions supplied by the architect"

Thanks for your help.

Dennis Pataki
Spring Grove, Illinois

Brad White_130

\"conditions supplied by the architect\"?

Mmmm. What do they know about heating?

Seriously, the lowest pressure rule always makes sense especially in residential systems with cast iron radiators. Commercial and institutional systems are different beasts.

The principal difference is the use of control valves. These valves have pressure drops (needed to establish their authoritay!) of between 3 and 5 psig. That is a penalty right there but without it, the downstream process cannot be controlled. Steam to water heat exchangers often are rated at 2 psig in the shell so add that in. "Wing" coils and other IFB coils often require 5 psig in the coil for various reasons, freeze protection, trap operation among others.

Many systems of these types operate at between 8 and 12 psig at the boiler. Most commercial low pressure systems are limited to 12 psig operating pressure so as to provide a cushion or margin to the 15 psig relief valve.

Your "1 psig at the farthest radiator" is still a tad too high in my opinion. In a home system it would be ounces and frankly, atmospheric if not a vacuum. The terminal equipment conditions will govern.

But your point is well-taken! The pressures should be as low as possible to do the job. Just higher in the systems you are describing compared to standing cast iron.

Hope this helps-

Brad

Pumpguy

Fan coil steam temperature

Thanks Brad for your reply.

I sell vacuum pumps for steam systems. I have a devil of a time convincing people that the first thing they need to do is to cut back the steam pressure.

Dennis Pataki
OAK SERVICES COMPANY
Spring Grove, Illinois

EBEBRATT-Ed

Brad,

I also have known that on low pressure steam that you should not run more than 12 psi for the reasons you have mentioned. I always find low pressure steam systems running at 13-14 psi. I always explain to the boiler operators that they shouldnt run over 12 psi

I read this somewhere in some code but can't find it and can't remember where--can you help me out with this ?????............

Thanks,

ED

Brad White_118

Sorry Ed

Not in any code I know of, but my experience and those of great steam equipment reps (Boyd Martin, Martin Engineering, representing Spence Regulator and Lonergan) always insisted. The tolerances on a 15# ASME relief valve being what they are, they always seem to "weep" at about 14 lbs.... I figure that speaks louder than any code. Always seemed like common sense, anyway.

Now, it may well be that it IS in a code somewhere, just that I have never seen it. If you find it, let me know?

S Ebels

Most fan coils I see

Most of the coils I see have been rated at 2PSI steam.

EBEBRATT-Ed

Brad-

I think it is code somwhere and for some reason 12 1/2 lb. is stuck in my head. I think I read it somewhere years ago but can no longer find it.


Ed