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HVAC Calculations and Sizing.
For many years we have worked on simulation services for the building industry. The services are based on software for sizing of HVAC systems and simulations of climate in building construction. The simulations of climate and comfort in buildings are based on software developed by the Royal Institute of Technology in Stockholm (KTH). The software was developed by Gösta Brown and Engelbrekt Isfält and thus named BRIS (light wind), BREEZE in English. They were assisted by Axel Bring, a key software developer and specialist, who later got an honorable Phd for his work with BREEZE. One major result of simulating comfort and climate has been enormous energy savings and revelation of the inadequate traditional sizing of insulation and HVAC.
The traditional sizing calculations were and are based on U-values and simple calculation based on a linear relation between outdoor and indoor temperatures with steady state conditions. The method was introduced in the 1920's, to provide engineers with a tool to obtain rough estimations for sizing of insulation and heating systems. Also, the assumption at that time was that we had an abundance of cheap energy resources. It is very important to note that the development of the simplified calculation method was for heating needs and was not meant to be used for cooling. There are no building codes or simplified calculation methods that provide any serious scientific guidance on sizing of cooling systems.
The weakness of the simplified calculation formula is very easy to show:
In an office of 10 sq m, built with today's building codes, the energy losses are around 10 W/K. During a working day, the loads for lighting, machines and people can be 350-600 W and solar gain through windows, 700-1,000 W. In a simplified calculation with steady state conditions, the rise in temperature would be 135 centigrade. It would be very difficult for a person to survive longer than minutes. Common sense and experiences must tell us that this is not happening. However, we are still sizing the HVAC system and controls for this case. It leads to a common over-sizing between 2-5 times what is necessary and to conflicting control policies that create enormous waste.
Correct manual energy transmission calculations are complex for most people and only one calculation takes a long time to do and will still provide large discrepancies between the calculation and reality. The difference between the simplified calculation and the correct one is much smaller than both are to reality. Because of the difference between calculation methods, it was assumed that the simplified calculation was good enough. But the large disparity was ignored. It is very easy and logical to explain why such a large difference exists. The current methods are based on air temperature, which contributes only one quarter, or less, to the humans body's perception of comfort. The total effect of the weather is often not correctly covered, the effect of the buildings emission/storage capacity is mostly ignored and the interaction with the human body forgotten (this is the nice and technical way to explain the situation).
The only way to get close to reality is by simulation, including that of the human body, weather, emission/storage and the continuous influence of the HVAC system. It was recognized at the time the simplified calculations were introduced that a manual simulation was almost impossible. But this was 80 years ago, when computers did not exist. Hundreds of calculations were needed just to get to a starting point where the subject could be studied, and hundreds more for the study of how the object behaves. This is because the variations in weather conditions and the emission/storage capacity of the construction. We have been able to do some comparative calculations and in those are included some of the most commonly used programs in the US. In the following diagram, we identify only BREEZE, since our point is not to disqualify specific programs but rather to show the differences in philosophies between correct transmission calculations and correct simulations.
Needless to say, almost all programs can show good relevance with reality, because the control system and policy comes in and makes the calculations fit. The equipment and control systems are designed to keep more or less constant temperature and the equipment is oversized. This means that the HVAC systems will contribute to and waste energy in line with the calculations in their attempt to keep steady state conditions. It will also cause artificial peak demands instead of showing how they can be avoided. All programs are a significant improvement compared with simplified manual calculations. Most serious programs do consider the sun radiation and to include the most common manual sizing methods in the diagram, would give an almost ridiculus result (as ridiculus as the methods).
The group behind BREEZE started around 40 years ago to do simulations with the help of computers and could, in a later stage, also include a measurement of the reaction of the human body to the environment. The result has been spectacular for Sweden. The original group of Brown, Isfält and Bring got the Swedish Energy Award 1992, for the work. It has also put Sweden 8 to 20 years ahead of the rest of world in energy saving in constructions.
BREEZE was running on a home-made computer called TRASK at KTH. At the beginning of the 70's, Teddy Rosenthal and I became aware of the vulnerability of this situation. We decided to migrate the software to a standard programming language (FORTRAN). Teddy, who at the time worked during the week with our group on stress calculations for piping systems in nuclear power plants for ASEA (today ABB), did most of the coding on weekly 3-hour train rides and lonely evenings at his hotel room. Teddy's work and the importance of it cannot be overvalued. He, more or less alone, saved a very important program for the research community and made it possible to continue the research for KTH. The result was a FORTRAN version of BREEZE that became very useful for us and essential for KTH when the TRASK computer was abandoned.
During the last 40 years, BREEZE has produced thousands of buildings that not only achieved spectacular energy savings, but also improvements in climate and comfort; this when the rest of the world still used the formulas from the 1920's and, in the best cases, correct transmission calculations by computers (with different degrees of adjustments to realities). Correct simulations are still very rare and you will not find any other program with the amount of verification and completed building projects.
We are currently investigating how we could produce an English version of BREEZE with English instructions. We have the rights to BREEZE, so that is not the problem, it is rather a problem of funding of resources and costs. Although BREEZE is a research program and the user interface is not designed for commercialization, it will be available free for research institutions and a small contribution to the translation costs for commercial usage. Education and support will follow the same lines. Our goal is to offer a way to calculate and study buildings behavior and to make it available for a larger research and engineering community.
We can handle only a very limited number of simulation projects due to the local demand in Sweden. At the moment we have to charge our going rates. It would not be fair if we charged one price to our current clients and a lower one outside of Sweden. We will however investigate if we can find a low cost way of performing calculation services that require less work from our side in preparation and reports.
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