District heating for a conference center.

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churchillrow

Member
Hearth Supporter
May 21, 2008
56
Northern Nova Scotia
Hi all,
Been a while since I've posted, got the boiler and tanks into the basement and then went back to my lurking ways in preparation for a system design post. In the meantime a friend of mine who is on the board of the Tatamagouche Center (http://www.tatacentre.ca/) and I got to talking along with a few others about a wood fired district heating system to help them with their $30 000 plus annual oil bill. Right now here in Nova Scotia there is a program- The Environmental Technology Fund (http://www.gov.ns.ca/ecoNovaScotia/pdf/EcoNovaScotia-ETP-Guidelines.pdf) which will help make this possible. I don't have good numbers for the peak heating load but some very rough calculations based on degree days, oil consumption etc.. show 200-300 000 btu distributed through 1 main and 5 smaller buildings.

Anyway the long and the short of it is I'm wondering if there are any engineers out there that are able and willing to work on a project like this. If any one has any names it would be much appreciated.



Thanks,
Augie
 
churchillrow said:
Hi all,
Been a while since I've posted, got the boiler and tanks into the basement and then went back to my lurking ways in preparation for a system design post. In the meantime a friend of mine who is on the board of the Tatamagouche Center (http://www.tatacentre.ca/) and I got to talking along with a few others about a wood fired district heating system to help them with their $30 000 plus annual oil bill. Right now here in Nova Scotia there is a program- The Environmental Technology Fund (http://www.gov.ns.ca/ecoNovaScotia/pdf/EcoNovaScotia-ETP-Guidelines.pdf) which will help make this possible. I don't have good numbers for the peak heating load but some very rough calculations based on degree days, oil consumption etc.. show 200-300 000 btu distributed through 1 main and 5 smaller buildings.

Anyway the long and the short of it is I'm wondering if there are any engineers out there that are able and willing to work on a project like this. If any one has any names it would be much appreciated.



Thanks,
Augie

Visit Garns website at www.garn.com They did all the engineering and supplied the equipment for a similar project in the Rocky Mountains. In fact, here's the specific link to the project. (broken link removed to http://garn.com/content/ucross.aspx)
 
Don't know of any engineers offhand, but it certainly sounds like a Garn job...

Gooserider
 
I've been working with a public institution that just made the shift this heating season from an LP multistage boiler system to a wood boiler system using a Wood Gun E500 (500,000 btu) and a Garn WHS 3200 (950,000 btu). The LP boilers remain for backup.

Discounting the issues caused by the installation contractor, I think it is fair to say that each wood boiler system has its advantages and each has its disadvantages, and that in this installation there may be distinct advantages resulting from having both types of wood boilers on line, as their operating characteristics are different and may allow for more flexible response to the wide range of heating demands in this cold northern MN environment.

The issues caused by the installation contractor may have somewhat clouded the expectations of management in making this shift. Regardless, management has realized substantial savings in heating costs this season, is still on the learning curve for most efficient operation of this system, and is committed to meeting heating needs in an environmentally sustainable manner.

Without knowing many more facts about your heating needs, how they currently are being met, staffing availability to tend the heating system, type(s) of heat emitters you employ, and more, it would be impossible for me to clearly recommend a Garn-type wood boiler or a large capacity gasification Wood Gun-type boiler. Real world use of either of these types of boilers is more complex than simply picking one or the other based only on a heat load estimate.

I note with interest the grant funding which may be available to you, which also was the case with the public institution. Due to the grant requirements, and the prospect of additional grants to make further progress on use of sustainable energy, the public institution may be installing additional control and monitoring systems to allow it to provide real world operating data which will be of benefit both to influence public policy and to assist other large institutions considering a shift to sustainable energy use. You may have a similar situation, and including these in your application for funding may be of benefit to you.

If you wish to discuss this further, you may send me a PM with contact information.
 
For institutional heating, it's pretty common (here at least) to use automatically fed gasifiers that burn wood chips. Pretty hard to find someone who will tend a large logwood boiler.

If your average load is 250,000 BTU/hr then your peak is likely around 500,000 BTU/hr. Those numbers could put you into the lower end of auger-fed chip burning systems.
 
jebatty

I have often thought that the ideal setup for a large load would be somewhat as you described if it was piped up and controlled correctly. There are a host of issues that need to be considered in any install, large or small but one thing that is common to installs using a large volume of storage is slow system response from a water temp standpoint. The integration of a lower water capacity boiler alongside the storage type unit(s) can help eliminate system lag when water temps are allowed to drop in the storage for whatever reason. The system could certainly be designed and controlled to take advantage of the operating characteristics of both kinds of units. The execution of the design and installation would undoubtedly be more complex but may indeed offer tangible benefits if done right.

I'd love to see what issues were present in the system you are referring to and what has been done to correct them. If you are free to discuss the details please share what you ran into.
 
heaterman said:
jebatty
... There are a host of issues that need to be considered in any install, large or small but one thing that is common to installs using a large volume of storage is slow system response from a water temp standpoint.

Count me as curious on this point as well. I've heard this complaint as a point against storage, but it seems to me that it's pretty simple to design a system so that storage is 'out of the loop' when it's not needed. Both the primary/secondary and simplest pressurized storage stickies accomplish that, and Tarm has another elegant approach using a diverter valve. Are there reasons why these approaches don't scale to larger systems?
 
Augie, these guys do the sort of thing you are considering with KOB boilers from Europe. They are very highly engineered wood boilers. I don't know anything about them personally, just ran into their website while noodling around. They're out in BC, I think. Timber industry oriented. Might be helpful.

(broken link removed to http://www.finkmachine.com/wood_boilers.html)
 
Heaterman, you have nailed a key point inherent in my comment on the combined system. Perceptive on your part.

Since I was not the person responsible for choosing the systems, installing them, determining the control system, and now operating them, although I had plenty of input, I want to do the best I can to be objective in stating any of my observations, which to be fair, also are based on incomplete information. In any case, these are just my observations, and I do not judge myself to have been competent to do all of the above anyway.

The institution has two primary heated structures, each previously served by LP boilers in each structure and not interconnected. One structure has 5 staged LP boilers, and the other has a single LP boiler firing system (may be more than on LP boiler). This is a pressurized system. The two wood boilers were installed in a new, separate building, located about 60' from the tie-in point to one of the heated structures and about 150' from the tie-in point to the other structure. Each structure had its own control system, and install of the wood boilers required a more complex control system. Both heated structures are served primarily by hot water unit heaters, with some of these being on the cool side of fairly long zones. I don't believe either structure is more than average in energy efficiency.

Garn - disadvantage. Setting aside what I regard to be errors in the installation, which if corrected would at least to some extent ameliorate the one issue now mentioned, a disadvantage with the Garn results from 1) the need to use a hx to interface the non-pressurized Garn with the pressurized system, and 2) need for high temperature hot water in the unit heaters to meet demand, particularly at times when outdoor winter temps are in the 0F to -40F range experienced in this area. To my knowledge expected hx performance is a 10F approach temp. Operating the Garn to maintain a continuous 180F supply to the system requires continuous 190F-200F Garn operating supply temp to the hx, and this is not practical. This also defeats the purpose of the storage capacity of the Garn, as there is little effective storage in these operating conditions.

Garn - advantage. The mentioned disadvantage of the Garn diminishes as heat demand diminishes with warmer outdoor temps. The Garn will much better serve its heat storage function at times other than high heat demand. The Garn also provides some advantage in providing pre-heated water to the Wood Gun and to the system in high heat demand periods, including when supplemental heat is needed from the LP boilers.

System design flaw. One goal of the Garn/Wood Gun wood boiler system was to have the Garn also serve as peak storage for the Wood Gun at times other than high heat demand. Due to design flaws, IMO, this function will be met partially, at best, and little if any, at worst.

Wood Gun - disadvantage/advantage. These are pretty much the opposite of the Garn. The Wood Gun performs well to provide continuous high temp supply, and therefore does well at times of high heat demand. As heat demand drops, the Wood Gun begins to idle and idling increases as heat demand continues to drop. The goal of the Garn serving as storage was intended to allow the Wood Gun more continuous high temp operation, but this goal was not realized. Separate dedicated storage for the Wood Gun would be very helpful and increase the operating efficiencies and flexibility in use of the Wood Gun.

There are many other issues with each system, including how it was installed and the control system. At this time I would tend to put some of these other issues in the "learning curve" arena of wood boiler operation, although some may be more substantive. As I do not operate the system, without more information from the institution and personal verification, I do not think it is reasonable to comment on these now.

Overall - Operating the system as it now is along the lines outlined by Heaterman is the likely direction for the near future. The institution may be able to obtain additional grants, and much further discussion will result as to whether to expand the system in the Garn or in the Wood Gun with storage direction.

A large wood boiler system using round wood, which must be dry, is a large issue. This institution has available a relatively inexpensive "endless" supply of wood. This is the north woods of MN, after all. LOL. Labor in obtaining wood also is not a large issue. But the time to dry wood, the space required to maintain wood in the drying stage until it becomes usable plus current usable wood, protecting the drying wood from the weather, locating drying area space near the wood boilers, moving wood to the boilers, etc. have become a much larger issue than was foreseen. In the case of this institution, the issue is available land area.

Smoke/odor etc has not been an issue with either boiler. The boiler building is located close to occupied buildings.

Staff to fuel the boilers has not been an issue, except at night and some weekends. This is where greater storage capacity would be very useful, particularly in periods of less than high heat demand, as storage could be charged and then provide supply during non-firing periods. Currently the LP boilers supply heat at these times, and although large savings in LP usage are being experienced, greater savings are possible.

A caution for any person/institution contemplating a wood boiler install is the experience, more likely the lack of experience, of the HVAC contractor. Understanding of how these systems need to operate and interface with conventional boiler systems, including such "simple" things as sizing the hx, proper install of the hx, calculating head loss, flow rates, return water protection (Wood Gun), system shock to the conventional system, lack of modulation, high operating temps, etc. -- may not be within the experience or understanding of the HVAC contractor, and may result in design, install and control systems which defeat the purposes of wood boiler operation.
 
The Garn also provides some advantage in providing pre-heated water to the Wood Gun and to the system in high heat demand periods, including when supplemental heat is needed from the LP boilers.

I have to correct this statement, as it is not accurate in high temp demand situations. When demand is for 180F water, the Garn cannot function well to provide preheating. It can serve this function at lower temp demand situations.

EDIT - might still be inaccurate, more thinking is needed regarding the variety of operating circumstances.
 
Check out this website

http://www.biomasscenter.org/

There are several free downloads with great information on biomass energy that would apply to small district heating system. They also have a hand in a large number of school and non profit biomass systems and may be able to point you in the right direction.

The Danish District Heating Council was touring the Northeast US last year, they have long term experience with large district heating and a lot of equipment companies that supply all the specialized equipment are members

http://www.dbdh.dk/

If its a public building, make sure you locate a engineer with a Nova Scotia PE, as you will need stamped design. There are a couple of big firms with offices in Halifax, I think AMEC and Stantech, but the overhead will be high.
 
jebatty and nofossil, I am curious too. Response time should not be a problem unless storage is 'between' the boiler and the distribution. Normally, with storage independent of the boiler this is relatively easily accomplished by following our drawings or the Simplest drawing. In this way, you can send heat straight from the boiler to the zones and only 'extra' heat is sent to storage. How does this work with a Garn? Is the integrated storage between the combustion chamber and the load, or can you send heat straight to the load when storage temp is low and there is a call for heat?

As others have said, more typical for this kind of commercial district heating would be wood chips (or pellets) because the fuel handling is so much easier. Not a small thing when you are trying to generate that much energy. That being said, and depending on the Garn's ability to send heat straight to the zones, I think either the Garn or a big Wood Gun or a big EconoBurn with separate storage would be a good choice.

One important point is that as a commercial job, an ASME certified boiler will be required (or open expansion). If you use and ASME boiler there would be no need for the open expansion and heat exchanger mentioned by the OP. I am pretty sure that both the Wood Gun and the EconoBurn are available as ASME boilers. I do not know about the Garn, someone will chime in with that info soon, I am sure.

Sounds like a cool project, keep us posted.
 
BioHeat Sales Guy said:
If you use and ASME boiler there would be no need for the open expansion and heat exchanger mentioned by the OP. I am pretty sure that both the Wood Gun and the EconoBurn are available as ASME boilers. I do not know about the Garn, someone will chime in with that info soon, I am sure.

As far as I know, the Garns are always open-expansion, because the boiler itself is not sealed-- and thus a water: water heat exchanger typically is needed between the Garn and the load (I've always wondered if this could be omitted if the Garn is higher than all loads- but that'd be site-dependent).

BTW, kudos for being so comfortable recommending others' products in cases where they might be the best fit--that's a mark of a quality vendor/ sales strategy with integrity.
 
A few comments.................

One of the first questions I ask a potential customer is what they are using or going to use for the heat emitters in the system. That factor probably has more bearing on the anticipated design than any other factor. In a situation like you have there, I nearly always recommend the addition of some emitters that will function with lower water temps such as steel panel radiators or coils that will work with lower water temps. I often find that the emitters in commercial or institutional buildings have been sized to utilize maximum water temps. From an efficiency standpoint this is a mistake even with a sealed, gas or oil fired system as best efficiency even with those types of appliance are obtained at 140* or less. Provided of course the equipment can handle condensation. The use of lower water temps to increase efficiency is common knowledge throughout the heating industry but many times corners are cut in sizing due to budget constraints.

I'll be the first to say that a system limited to the use of water at 180* or higher is not the best application for a Garn. It basically defeats the purpose of not only Garn type storage but any type of storage it would be tied to. Storage is most useful when the system temps can be allowed to swing in a 40-50* range while still providing adequate heat. When the temperature operating band gets down to only 10-15* any practical amount of storage will be of limited use.

The best configuration I can see for the system you have there would probably be to use the Garn as the "base load" unit when temps are in a more moderate range. The Wood Gun could be piped into the pressurized side of the HX and operated via an aquastat or even an outdoor reset controller on the system return . One could play with the setpoint to find the optimum differential to "synchronize" the two units. A variable speed circ which looked at DeltaT might be the berries for keeping a steady load on the Wood Gun in that scenario............But I'm just day dreaming here. If I could lay my eyes on it I might have a completely different take on the situation.

If I were in a position to recommend changes to the system, the first would be adding output capability in order to reduce system operating temp constraints, that is, assuming basic piping deficiencies were addressed..
 
I thought this thread was dead. Thanks for the responses, for some reason I'm not getting the email alerts. Anyway I've got to digest all this.

Augie
 
After some reading I think I understand most of what is being said. I wish I had more info about the center to throw out there but this is still in proposal stage and we haven't gone to the expense of getting an energy audit. I'm not sure how the funding process will really work but it seems like we'll have to "come up" with some numbers for system requirements and costs and then reassess after we actually get some money to figure out what's required.

As to engineers I'd really like to stay away from huge outfit like Stantec. It my intuition the a design process with lots of iterations (including a few posts here ;-) ) would be hard and expensive that way and my experience with engineers doing something they aren't familiar with is that they tend not to be very subtle and overkill everything the first time through. Anyway thanks for the links, the search continues.....

Augie
 
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