updated steam systems in commercial buildings.

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hi. i am a residential oil burner mechanic,going for an interview for a position,of maintenance mechanic ,were i noticed the few buildings have steam boilers,and in every room the old castiron radiators have been removed ,and replaced by some type of square looking baseboard and have some blowers in it.also every room have thermostats.the buildings that i am talking about are schools.so there is no central ac.if any one can help me with the order of this type of operation.the buildings are 70 years old.i do not know if is a single pipe or two pipe system.

Steamhead

It's probably

some sort of 2-pipe system. The blowers probably bring in fresh air. 

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updated steam systems in commercial buildings.

thank you for your answer.i have 2 more questions.first i do not see any duct work,so i believe the blower are creating fresh air within the room for better quality of air ,because i do not see any openings from out side.2nd question is since every room has tt's i think the sequence of operation is similir to the zoning (zone valve or circ.)to an hydronic system in a residential set-up.if i sound silly excuse me i do not have a lot of experience in coomercial systems.i am just trying to understand in simple words the sequence of operations that triggers the burner to fire. thank you, very much.

Steamhead

In a school building

the law generally requires a certain amount of incoming fresh air. That's probably why the blowers exist. The amount varies from state to state- check with your Code authorities for details.



The boilers are probably cycling off some sort of outdoor control like a Tekmar or Heat-Timer. The room thermostats probably control a set of splitter dampers at each blower.



Not sure where you're located, but many school systems really skimp on maintenance, only fixing things when there is a crisis. You may find you have your work cut out for you in this job.

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updated steam systems in commercial buildings.

thank you for your help.I have a good picture now of the system.

HarryR

Could be a hybrid

Hi,

     This sounds very much like a type of hybrid steam/hydronic system I see often in the mid-Atlantic region. A steam boiler powers a heat exchanger in the boiler room, sending hot water up to fan coil convectors in the living areas. The convectors use wall mounted thermostats to control the fans and hence, the room temperature.

     Look for a heat exchanger in the boiler room.

Dave in QCA

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Brad White

Sounds like

a unit ventilator job. The cabinets are typically 16 to 22 inches deep, 25 to 30 inches high and with lengths ranging from five to eight feet depending on capacity.



Brand names you may find on the cabinet or internally might be Herman Nelson, Nesbitt, McQuay. There is another name I cannot recall, an obsolete name no longer in business, a Germanic name beginning with Sch... not Shumacher, but longer and with more syllables.



These unit ventilators are very common in schools and a tell-tale sign are grilles or louvers on the outside of the building walls against which these are installed. The grilles tend to be horizontal, 8 inches high and 32 inches to over five feet long, roughly. (Dimensions tend to conform to masonry unit dimensions.)



They still make them and they are often the lowest cost denominator on many projects, providing heating and ventilating (sometimes and rarely AC in our northern climates).



A typical steam unit ventilator would have either a diverting mixing damper or a face and bypass damper, sending a portion of outside air through the coil and bypassing the rest based on space temperature needs. Regardless, a minimum cfm of outside air per student is maintained, by code. This varies, but 15 to 20 is a typical value depending on which code or reference standard is used. (ASHRAE 62.2 usually.)

 In warmer weather, these unit ventilators can deliver 100 percent outside air and have inherent "economizer" capability to mix OA and return air for free cooling as needed. This is known as the ASHRAE II cycle by the way, sort of a "Canned" sequence commonly applied.



Big as they seem to be, they pack an awful lot of stuff into those cabinets.



Anyway, a bit of background you may find helpful, or by now, may have heard elsewhere.

ttekushan_3

school steam, t-stats

The thermostats may well be pneumatic. If there is an air compressor near the boiler room, this is what it is for. I know many people dislike pneumatic thermostats, but what I like about them is that they can modulate the heat in incredibly small increments. In other words, the steam supply valves can be partially open with purely pneumatic thermostats. It seems that the real keys to pneumatic longevity is that the air tank has an automatic water drain, and that the air supply has good dryers.



Also, many schools with steam heat have vacuum return pumps.