Steam Coils and Freezing

[osiyo]

With 100% steam MAUs the F&BP dampers require the linkages set right when dealing with extreme lows. With 100% steam F&BP MAUs I always had the steam valve 100% open below about 45-50 F OAT. Above that I modulated the steam valve.

Yep, typically what we do. We use a bit lower OAT before we switch over what we're modulating, but same idea.

[osiyo]

Awesome info. Thanks guys.

One more Q...

On a steam valve running 100% open (MAU face/bypass setup). What would cause the coil to make tinny-pinging noises?

Without hearing the precise noise, I wouldn't know for sure.

But one will generally hear some pinging due to droplets of condensate forming, they get flung around pretty well when steam valve is wide open continuously. Assuming you've got the normal building heating type steam system with low pressure saturated steam.

For power systems using steam, running high pressure super heated steam, yah don't want to be hearing any pings from droplets condensing in a turbine. That'd be BADDDDD. Would be time to shut down or run. And maybe too late to do either. BTDT. Didn't like it, not even a little bit.

[Noel Murdough]

9 on the clenched sphincter scale?

[osiyo]

9 on the clenched sphincter scale?

Chuckle, more like an 11 on a scale of 1 to 10.

It slammed shut so hard and fast, it clanged like dropping a cast iron skillet on a steel deck.

Fortunately no one got injured. Had to replace some blades on that turbine tho.

[i b cool]

If coil is not pitched properly it may be holding condensate, this may cause pinging and also could be more prone to freeze.

[madhat]

The old Worthingtons actually had freeze-plugs on the coils. I think they put themselves out of business, stuff was designed/built too well and they didn't sell enough parts.

On my Hot Water coil MAU, anytime the fan is off the outside air dampers close. "I cut the 120 vac to them. A bypass relay, let's the duct stat(s) alone control the unit temperature. if you open the unit after a freeze-stat trip, it's nice and toasty in the unit. I also doubled up on the freeze-stats.

[ctrlguy]

What's the point of trying to heat with superheated steam? You won't get any significant BTUs without condensing the steam and you won't condense the steam until it wends its way through the coil a ways, so you won't get as much heat out as you would saturated steam.

Tube within a tube steam coils are pretty common for one reason: Steam coils are really easy to freeze.

[Freezemeister]

Steam is a method of moving heat from one place to another. when steam condenses it gives up the BTU's of heat that were added when the steam was made. Superheated steam has more BTU's, so more heat.