Single-Source Solutions: System Modeling (January 2001)
Analyzing Data And What If'sSystem modeling is the application of computer software for analysis of various mechanical and electrical design parameters, building systems, and building construction. The Department of Energy (DOE) has its DOE-2 program, while a few major equipment manufacturers have also invested in the development of their own system modeling software. This engineering tool includes the building design parameters such as lighting watts per sq ft and internal equipment load (copy machines, computers, etc.), and number of people in the building, hours of occupancy, etc.
Another part of system modeling is to insert the types of hvac equipment and system options that could be provided to service this new or renovated building. The system modeling can simulate a number of "wet" systems (centrifugal chillers, heat pumps, thermal storage, etc.) and also a number of "air-side" systems (variable-air volume, reheat, double duct, etc.). Along with system analysis, the software should include the operational costs associated with each of these systems, first cost, operation and maintenance cost, life-cycle costs, etc.
I have been using this building design tool since a building program in which the owner wanted the facility "to be a national example of energy conservation." At the time, we were in the infancy of energy conservation with the country experiencing, for the first time, long lines of cars waiting to fuel up at the gas pumps. When I first used this system modeling, the average office building in downtown Boston was operating at about 100,000 Btuh/sq ft/year for an existing building and around 75,000 Btuh/sq ft/year for a new building.
Based on the computer software simulation, we came up with a new office building at around 56,000 Btuh/sq ft/year. The facility when eventually brought online operated at around 44,000 Btuh/sq-ft/year each year for the first five years. After that, I lost touch with it, but was satisfied that we had exceeded the building program and owner's goal.
System Modeling Can Give An EdgeThis first experience gave me the opportunity to learn the value of system modeling and how this information can contribute to determining the operating budget for a building program. Interestingly, between the 1970s and the 1990s I seldom saw this computer software used as an integral part of a program's criteria the way it was mandated by our customer back in 1977. It wasn't until I joined a company in the mid-1980s that did outsourcing, as well as design-build, that I saw system modeling filling a void that the design engineering community all too often left out of building design. At the time we would forecast the operating budget, which was so important to our outsource company, as they strive to have the competitive edge over the building owner's facility group performance.
This understanding of operating cost proved to be invaluable as a design tool in the years to come as it consistently provided me with the engineering, "big picture" vision of building performance. It also gave me a better appreciation of how facility engineers could contribute to the building program, year after year, if given the opportunity to manage mechanical and electrical energy-efficient systems. Today we have historical data to benchmark from various organizations to monitor and measure building performance such as the DOE, BOMA, and ASHRAE.
Based on this available information, building programs should be including operating budgets into the initial program management phase of their building program. Unfortunately, building programs miss this "line item" in the cost of the building over the life of the building. At the same time, design-build engineers are not injecting system modeling into the building program. The focus shouldn't continue to be "first cost" while the building program misses the opportunity see the "big picture" vision of system modeling. ES