City Steam and One Pipe System

DaveGateway

We are working with a customer that has a 6-story office building in Kansas City. The building has cast iron radiators and a 1-pipe steam heating system.

The building used to have a stand alone boiler. Now the building gets its steam from Trigen, the city steam provider.

Trigen provides steam at 12 psi.

The building has not heated well since the switch to Trigen at 12 psi. Trigen will only provide steam at 12 psi. Condensate is wasted to drain.

We know that we should be operating at 0.5 to 1.5 psi. Does anybody have any experience on the best way to regulate the steam pressure and control the system for it to breath in and out as a 1-pipe system needs to do?

Unknown

You'll need a pressure reducing station,

and you'll need a thermostat in the space someplace to cycle a valve open and closed, which will allow the system to vent air and breathe air back in.

Thermostatic radiator vent valves would give room-by-room control.

A bonus system, which would control how much steam is used very carefully, is made by tekmar, or Heattimer.

These controls are different from each other, and would be selected depending on the specific set-up that you have.

http://www.heat-timer.com/?page=steamheat

http://www.tekmarcontrols.com/products.html

Noel

Joe Lambert

Reduce the pressure

Definately reduce the pressure with a pressure reducing valve. Here in NYC our company uses Spence pilot operated PRV's. We install a solenoid in the pilot to use as a safety shut-off and control for on/off systems. We also install modulating valves - AFTER PRESSURE REDUCTION - if the building wants that type of control.
There are other manufacturers as well, but to start, look at: http://www.spenceengineering.com/Handbook/ed_series.pdf

Unknown

High pressure steam to low pressure steam

You need to install pressure regulators or pressure reducing valves in your building.

Pressure regulation can occur via the use of two properly sized motorized zone valves or a pressure reducing valve station using twp PRVs to lower the steam pressure to the pressure you need to operate the building.

FRor this installation you must have an engineer that understands steam heating.

The valves need to be sized correctly or you the valves will eventually wind up with wire drawn seats or steam velocity noises accross the valve may become a problem.

In any event, Sarco and Spence valve companies make controls that will open and close the PRVs when steam is needed to heat te building. Additionally, the building temperature control should be put on a Zone or zone valves with Heat Timer or Tekmar panels for temperature control.

I am supprised that a supplier of centralized steam did install the reducing valves. If tha system becomes damaged because of the suppliers failure to reduce the steam pressure they can be held liable for damages.

Because they took the contract to provide heat in a safe and dependible manner they should install the reducing station.


Jake

Dave_12

City Steam & 1-Pipe Systems

Thanks for the input on this subject.

We will propose the the owner to add a Watson Mc Daniel "D" type pressure reducing valve with solenoid pilot. That, along with the existing motorized valve and a pressuretrol, may solve the problem. We will install the pressuretrol downstream on the steam main serving the building and wire it in series with the building thermostat, and then on to the motorized valve. The pressuretrol will be set initially to cut in at 0.5 psi and cut out at 1.5 psi (and adjusted if necessary from these settings). This way the system will be controlled by a pressuretrol just like if there was a boiler in place, cycling between 0.5 psi and 1.5 psi as long as there is a call for heat. When the building thermostat is satisfied, the motorized valve will close.

As a low cost alternative, we also considered just adding just a downstream pressuretol and wiring it in series with the building thermostat to control the motorized valve to a downstream pressure of 0.5 psi to 1.5 psi--any thoughts on this cheap & dirty fix. Has anyone tried this. Will it over shoot?

Again, thanks for the help.



Dave

Unknown

Ouch

Don't do it.

The valve would try to be the regulator.

You would hate the noise, me thinks.

I'd set the regulator to a pound, and let the thermostat open and close the valve, myself.

Follow the instructions for the regulator in sizing and location relative to the valve.

Noel

Jamie Hall

Amen, Noel

Even if you enjoyed the noise on that arrangement, the frequent (probably VERY frequent) cycling of the valve would destroy it in no time flat. Go with a properly sized pressure reducing valve, but get a really good engineer who understands steam (as someone said earlier) to size the thing -- saturated steam just doesn't behave the same way through a valbe as do air or gas, never mind water.

flange

in this case, you will need to add the reducing station. i'd be very careful of the t-stat location, as you really want this thing to cycle to allow for proper drainage of the condensate. thermostatic air vents might be nice for regulating heat in some areas. as far as the condensate, i cant believe you are just dumping it down the drain. as a value added service you may ask your customer to consider using a heat exchanger to temper the condensate and produce domestic hot water during the heating season. that steam from the utility holds a lot of btus. why not use them up? remember, it is probably generated at higher than 12 psi and reduced at your building. this means you have superheated low pressure steam right?? the more energy we can use up the better it is for all. if you are dumpimg condensate higher than 140* you are probably violating code.