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Abstract, BREEZE simulation program.
The BREEZE program is based on a heat balance method where finite differences are used. In documents describing the physical basis, a simple derivation is presented in which the heat flows are defined in terms of the temperatures both at the beginning and the end of each time step. This approach (according to Crank-Nicolson) was adopted already from the beginning in the early sixties. No method has been used aiming at short computing times e.g based on the response factor principle.
An iterative method like that applied in BREEZE, yields a good calculation accuracy. Linear modeled processes are not required. Inside surface heat transfer coefficients being dependent on the difference between surface and space air temperatures can be expressed in a proper way during varying conditions.
Another benefit from the iterative procedure is reached in BREEZE by the use of the variable "quantity sought". It is evident from its code structure that the HVAC system is included in the calculation. In several other programs the calculation is divided up into steps and the performance of the building is first determined without consideration to this system. The calculated heating or cooling rates are then used to select the system components that are necessary to fulfil the specified comfort demands. In this procedure the feedback is neglected, that is obtained by the interaction between the building itself and the HVAC system.
The radiation from windows affects the thermal climate in a room, both directly and indirectly, and is therefore given great attention in the program. Occupants feel easily the heat or cold from the inside surface of windows, and this is noticed by calculating effective temperatures and "comfort numbers", taking the window surface temperature into consideration.(The BREEZE model of effective temperature is introduced in Swedish building regulations, in a little modified form.) Daylight intensity can be determined if desired, necessary for estimating the times of the day when artificial light is needed, and the energy requirements for this light. A very important heat balance factor is the insolation energy coming from sunlit windows and stored in the building structure.
A difference between BREEZE and most other well known programs might be that the heat flows to or from the room surface layers are recorded as a part of the room heat balance. They are often a dominant item in this heat balance. In an example is shown how moderate cooling power can be sufficient, if a small rise in effective temperature is permitted during working hours even in summertime. This cooling effect by the building structure is reached especially when the ventilating system is running during the night and chilly outdoor air cools the room surfaces. This practice of running ventilating systems is not unusual in Sweden, possibly with a view to avoid the demand of air cooling equipment wholly.
In a hotter climate, for instance in many parts of the USA, this way of utilizing the thermal capacity of building structures for moderating temperature oscillations is often not sufficient for making cooling equipment superfluous. Many BREEZE runs have shown, however, that also in such cases the demand for air conditioning is reduced, with equipment first cost reduction. Significant energy savings are also realized by utilizing the building dynamics and systematic peak demands are avoided.
A computer based calculation method, where the principle of low amplitude indoor temperature oscillations with equipment of prescribed capacity is applied. Examples show how the probability of the occurrence of high effective temperatures in a room can be estimated, with assumption of relevant outdoor temperature statistics.
The manual calculation procedure by use of nomogram, shows that it may be possible to create simpler ways to solve thermal design problems, not necessarily bound to lead to larger approximations, that is when they are directly based on an accurate computer method. The advantage of this graphic solution is not only that it is cheaper and more rapid to use, it also indicates more directly the connection between the parameters included. Especially at an early stage of design work, this can be of great value.
The BREEZE program has been extensively used in research work and technical development studies, as well as in building design. Experience is thus obtained from projects as office buildings, schools, hospitals, etc.Examples are: The new (temporary) Parliament Building and the renovation of the old Parliament Building in Stockholm, buildings at the International Airport of Stockholm (Arlanda) and the new SAS-hotel in Oslo.The validation of the program is thus confirmed by feedback from its use in connection with over one thousand of building projects, besides by results from laboratory measurements( see e.g.Brown,1972). The ventilated floor slab construction has been chosen in about 400 buildings. The numbers were actual for beginning of the 1990's, today (2002) the numbers has grown at a significant rate and are probably 3-4 times higher.
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