Coming up with a solution of boiler control and fuel costs was one part of the horticulture solution. We also had space limitations, fuel delivery and storage issues, and tying the project into the educational mission of the Arboretum. As a showcase to the public, the Arboretum strives to introduce the general public to more efficient and sustainable technologies. We had known that in parts of Europe commercial/small industrial wood pellet heating systems had been in use for years. Home heating pellet stoves are very common in Northern Arizona, yet few people had experience with trying to heat larger buildings with wood pellets.
 

Forest Energy Corporation in Show Low, Arizona offered a boiler from Tarm, USA which imports wood pellet boilers from Denmark. After some research, we decided to install a Tarm 4.0, a 136,000 BTU boiler into our 3500 square foot building. The horticulture building is currently filled to capacity with plants and people, so we had to find a home for the Tarm. We wanted to keep our existing boiler for a backup system, so we ended up enclosing an outdoor space just outside the boiler room. Space limitations and boiler setback requirements took some creative thinking but at least we had a plan. The last remaining hurdle with the project was what to do with the onsite storage of wood pellets.

Forest Energy wanted to deliver pellets in bulk, so they proposed a 22 ton silo to be placed next to the building. We had concerns with the fact of having a tall silo in our gardens and the cost of the whole silo system was well over $20,000. This put the whole project out of our budget. We decided not to go with the silo and went with the system of hand feeding the boiler with 40 lb bags of pellets. So for now we will receive several tons of bagged pellets and will store these at our maintenance facility. Once a week, we will haul 25-30 bags of pellets and add an average of 3 bags per day to the boiler's hopper. A filled hopper (16 bags) should last about four days. At least now we can leave the boiler running 24 hours a day, and should be able to leave during weekends and holidays! We can also heat the entire building and our heating cost should drop. I would forecast that we will use 2 tons of pellets a month. Bagged pellets are $180 per ton.
 

So heating should cost about $360 per month. Remember that propane was costing about $510 per month for the 2004-05 heating season.
 

Installing the boiler was surprisingly simple. The most difficult part was moving the 1500 pound boiler into the small enclosure. Ted Wyatt of Wyatt Development, Inc. installed the piping and wiring. On April 6th we fired the boiler for the first time after the county building inspection. Our storage tanks came up to temperature in 9 hours, providing 130 degree water to heat the building. A week of warm weather caused us to shut down the system but during the following week colder weather returned and we fired the boiler back up. We will shut down the system for the summer and plan on waiting for colder weather next fall to see what the system will really be like. I will be posting more reports during the heating season of 2005-06.