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February 10, 2009
Cogeneration Feasibility
My 96 unit condo association consists of two circa 1923 five story courtyard buildings which currently share an oil fired furnace to provide one pipe steam heat to both buildings.
The buildings operate the steam system from a central boiler vented to an interior courtyard and individual hot water boilers in each building. There is a very large smoke stack as part of the original coal fired furnace which was abandoned in the late 1940s when the system was converted to oil.
As our boiler is close to 30 years old now, the association wants to convert from oil to high efficiency gas. Doing so will require us to restore and reline the old smokestack and totally rework the existing boiler room.
Since this is a major project and we do have such a large stack, I was wondering if anyone had ever had a cogeneration system installed with such a setup?
Comments
Why not dual-fuel boilers? You get the lowest possible gas rate. Is co-gen is cost-efective for your relatively small size?
Posted by: BH76 at February 10, 2009 12:40 PM
Dual fuel is a problem, because the oil tank is underground and probably won't maintain its integrity much longer. The gas conversion is to lower fuel costs and prevent a costly environmental cleanup in the future.
I'm asking about cogeneration because the buildings currently go through 20k of electricity in the common areas, elevators, exterior lighting, etc. a year. Since the boiler is on for a good part of the year, generating our own electricity could be worthwhile. Well, that is if the cost to install and maintain the system, is recouped by the savings on the common electric bill.
That's part of why I'm asking.
Posted by: FenFen at February 10, 2009 12:59 PM
Microturbines would be the way to go. I'd be very interested in the economics of your project. They produce hot water, not steam, so you'd have to pipe them past the individual boilers.
A 75kW cogen unit can provide 490kbtus, you'd probably need 2 for 96 apts...
http://www.tecogen.com/pdf/cogen4pg.pdf
Posted by: cmu at February 10, 2009 1:21 PM
Are you planning on switching from steam to hot-water heat in the process? "High-efficiency" steam boilers don't really exist, as I'm sure Master Plumber will tell you in greater detail.
Also, your current oil fired boiler vents into a courtyard? Isn't that kind of unpleasant for anyone with windows on the courtyard, fumes-wise?
I've always found co-gen intriguing...keep us posted on your findings.
Posted by: arches at February 10, 2009 2:07 PM
Interesting idea, here is a link to what looked to me like some useful information:
http://peswiki.com/index.php/Directory:Home_Generation:Cogeneration
They seem designed to put out alot of heat and a little electricity. You might have a problem in the summer.....
Posted by: slopenick at February 10, 2009 2:19 PM
The courtyard is completely enclosed and the size of a basketball court. The soot can be terrible when it doesn't rain for several days.
Posted by: FenFen at February 10, 2009 3:17 PM
The courtyard is completely enclosed and the size of a basketball court. The soot can be terrible when it doesn't rain for several days.
It would probably be prohibitively expensive to change our one pipe system to two pipes for hot water. Additionally everyone's kitchens and bathrooms have heat pipes, so heating with water would require all those spaces to be converted.
Posted by: FenFen at February 10, 2009 3:19 PM
As CMU states, a micro-turbine would be the way forward as it will offer you much more flexibility. The interconnection of the equipment with the utility is much easier as the micro-turbine produces high frequency AC power which is connected to the mains via an inverter, therefore no kVAR requirement. This system could also operate in isolated mode if you lost the utility service, provided it is connected in an approved manner. One disadvantage with the micro-turbine is permiting and fire regs. although this has got much easier over the last few years.
The tecogen standard 75kW cogen unit is also very good and very efficient. This is not a microturbine (although I think they do now produce one) but an induction generator driven by natural gas recipricating engine. Aegis Energy also produce a similar 75kW system which 523 gives kbtus/hour, also a very good system. This type of system always requires utility voltage to operate so cannot operate isolated. Also, because it utilizes an induction generator there is a kVAR requirement which can have an impact on your facilities power factor.
Neither the Microturbine or gas recipricating engines produce steam, they both produce hot water which can be used for heating / hot water in winter and airconditioning (via a heat exchanger) / hot water in the summer.
Posted by: BigBob at February 10, 2009 3:24 PM
I see, the cogen system would replace our central water heaters and vent excess heat out the shared stack with the new gas boiler.
Posted by: FenFen at February 11, 2009 10:23 AM
fenefen, That's confusing...with a cogen system you will not have a new boiler.
The single cogen unit produces hot water for space heating and electricity for whatever. As one is a byproduct of the other, you save energy costs. Additional costs are incurred due to the complexity of the unit and its controls, installation is much more complex and you have to check into ongoing maintenance and reliability issues as well.
Since your current system is one-pipe steam, as you said this conversion may not be feasible. There are industrial cogen systems that produce steam, usually hi-pressure (residential systems are low pressure), but are probably not applicable.
Is this bluesky or is your building seriously considering something like this?
Posted by: cmu at February 11, 2009 6:30 PM
With the amount of rooftop you must have, why not consider photovoltaic? Perhaps solar domestic hot water. I can discuss that with you...
Posted by: SteamMan at February 12, 2009 11:30 AM
Photovoltaic is out because the people on the top floor have roof rights to area directly over their units.
Right now a few people have added ladder access from locking closets to permit use of small roof decks over their units. Or they've added skylights in kitchens/foyers/etc.
Those whom haven't done so would probably be unhappy to lose their rights to develop parts of the roof over their units.
Posted by: FenFen at February 12, 2009 2:48 PM
yeah, a Microturbine is definitely the way to go
http://www.ingersollrandproducts.com/IS/Category.aspx-am_en-18218
Posted by: initd at July 24, 2009 1:04 PM
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