Load Calculations and Log Cabins

LOAD CALCULATIONS AND LOG CABINS©
by Bill Smith, president of Elite Software

Mark Sweptson, an Ohio contractor, routinely accomplishes the impossible in his high end projects, many of an unusual nature. One of his recent and most difficult projects was a $2,000,000 luxury log cabin home built into the side of a hill. Sweptson recalls, "It was essentially a commercial building at 10,000 square feet. The structure presented many problems we had never encountered before that required all our skills and expert use of good computer software."

Mark Sweptson owns Atlas Butler Heating and Cooling with annual sales of around $13,000,000.

The company of 140 employees was founded in 1921 and serves Central and South Central Ohio. Sweptson, a former ACCA Vice President, was named Ohio Small Business Person of the Year for 1997. Sweptson, the current ACCO president in Ohio, received this prestigious award from President Clinton in Washington, DC, in July, 1997. Sweptson and his company were judged on staying power, financial statements, sales growth, and innovative products and services, according to the U.S. Small Business Administration.

In 1995, Sweptson also received the Carrier Distinguished Dealer Award, a distinction earned only by ten companies in North America, chosen from a group of 8,000 dealers.

Originally began in December 95, Sweptson's log cabin contained many unique design problems. He recalls, "To build the house takes a minimum of a year, and it's better to take two, because the home continues to settle

during the building process. While building, the logs actually shrink even though they were previously cured two to five years to reduce the wood's moisture. Even after the logs are in place, the house continues to shrink substantially. Moreover, the logs don't shrink proportionally throughout the house. During construction, the four main support logs, each thirty six inches in diameter, located in the center of the home, were set on jacks. As the house settled, the jacks were adjusted so that the house would settle evenly as the house shrunk. All the plumbing and HVAC systems had to be installed with flex connectors so they wouldn't come apart as the house shrunk."

Sweptson says that the builder insisted on only exposed wood throughout the house to hide mechanical and other systems. He remembers, "Everything had to be in wood - even the walls were solid wood and there were no plenums. He did not want to see any kind of ducts or registers or anything exposed. To accommodate the mechanical, electrical and plumbing systems, the builder built one floor decking with exposed timbers underneath, then laid in all the mechanical and electric. He then built a pine floor on top of that which framed around the HVAC and plumbing. He then built a floor on top of it."

Sweptson uses Elite Software's load calculations (RHVAC) and energy analysis (AUDIT) programs on most of his projects. He explains why computerization was essential for the success of this project. "The log house was built into the side of a hill with the first floor completely underground and opening up to a sheltered ravine. It also had all masonry walls and lots of glass around it. Another important consideration was that the logs have to maintain enough moisture so they don't continue to dry, twist, bend and shrink after the house is built. The logs actually add moisture for the first couple of years and then they take moisture out of the air. This was an unusual and critical factor in our load calculations. Furthermore, to prevent additional shrinkage this home required a special humidification system."

"With solid wood walls 14-16 inches thick, we didn't fully trust the standard ASHRAE numbers", he recalls. "RHVAC let us quickly try many 'what-if' scenarios to test different system configurations so that we could optimize our design for both reliable comfort and energy savings. It was critically important in that it allowed us properly size the systems by individual zone. The program gave us the precision and speed we needed to repeatedly test for, and find, the best balance between removal of humidity from the logs and causing unwanted shrinkage."

In the final design, there were three systems in the house, each with two to four zones, for a total of 10 zones. He adds, "RHVAC easily allowed us to work with each "module" or section to fine tune our design. Without RHVAC, we would not want to think about the difficulties of this kind of project. Lastly, it allowed us to size the ductwork to keep it hidden yet serve the house properly."

Sweptson points out that he designs conservatively to make sure his clients are, first and foremost, comfortable. He continues,"We used Elite's AUDIT energy analysis program to try out different 'what if' scenarios for energy efficient systems as discussed with the builder. For example, if you did the standard load design you might have a six- ton load. Because the software showed we were getting a balance between the systems on the zone, we were able to go down to a five ton system. I didn't have to split it up with two three-ton units and we actually got better comfort this way. AUDIT's reports show in a clear and compelling way the advantages of different systems. They impressed the builder and made him feel very comfortable with our recommendations."

"In the old days, contractors would do one floor at a time or do the whole house as one zone just to get it done. They wouldn't consider all facings and do a complete design. With AUDIT, we can do a design section by section which helps us see the impact of those loads through the day."

"As a result, we put the master bedroom on its own zone and set up the other nine zones based on owner's living style. We put in a control system that gives them a set back control in each zone. And being a Carrier dealer, we installed Carrier MVP gas furnaces and Carrier TR 12 SEER air conditioners. AUDIT helped us with many energy saving features in the system although we allowed for plenty of cooling for key living areas based on their activity and the external loads."

Sweptson notes that without the power of computerization, they simply would not have taken the job. He explains, "We couldn't have done the job in as much detail as we like plus it would've taken more time. RHVAC and AUDIT allowed us to do the job in 25% of the time it would have taken to do manually."

"In addition, the professionalism of the programs' reports makes me feel comfortable when I go out to the client to make the sale. I also know the cost of the job in advance. In the past, we would only have a budgeted cost because we couldn't take the time on every job to do a full layout design before we got the job. With the software, we have the ability to size and cost the job in great detail, give the client options and quickly recalculate if necessary. That helps us get the job as well. We can win more jobs because we are more professional up front," he concludes.

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