7.3.1 Analysis method for building energy demand

A wide variety of building energy analysis methods are currently available to HVAC engineers and range from simple to sophisticated. The simplest methods involve the largest number of simplifying assumptions and therefore tend to be the least accurate. The most sophisticated methods involve the fewest assumptions and thus can provide the most accurate results. Generally, methods for building energy analysis can be categorized into three and are as follows:

• Single Measure Method (example: Equivalent Full Load Hours)

• Simplified Multiple Measure Method (example: Bin Method)

• Detailed Multiple Measure Method (example: Hour by Hour)

Here, calculations are made via detailed multiple measure method. In this method, energy calculations are on hour-by-hour basis. As a result, they have the potential to satisfy all the requirements listed earlier for high-quality energy analysis results. There is, however, a certain amount of variation among different detailed multiple measure methods, leading some methods to meet the accuracy requirements better than others. Within the detailed multiple measure category, there are two major sub-categories worth discussing: The Reduced Hour-By-Hour Method and 8760 Hour-By-Hour Method. In our calculation the second method is used. The 8760 hour-by-hour method

This method simulates building and equipment performance for all 8,760 hours in the year using the proper sequence of days and actual weather data. No weighting of results or simplifications are necessary. The fundamental principle is that the way to produce the most accurate energy and operating cost estimates is to mimic the real-time operating experience of a building over the course of a year. All the requirements listed earlier for high-quality energy analysis results can be met with this approach. The actual weather data account for the range and timing of weather conditions in great detail. Further, the hourly and daily variation of building occupancy, lightning, and equipment utilization can be easily accounted for. In addition, the full year simulation tracks the dynamic hour-to-hour and day-to-day thermal behavior of the building, and the response of HVAC equipment to this behavior. The ultimate result is high-quality data that can be utilized to produce accurate, detailed data about the quantity and timing of energy utilized. Both are requirements for accurate operating cost estimates (Pegues, 2002).

The 8760-hour method produces a diverse, realistic set of cooling and heating loads for the month. So in this study, 8760 Hour-By-Hour Method is utilized to determine the cooling load.

7.3.2. Description of the ACS considered

The present study simulates a building and an ACS which utilizes a solution of lithium bromide and water, as the working fluid pair (see Fig. 7.3). Water is the refrigerant and lithium bromide, a non toxic salt, is the absorbent. Refrigerant, liberated by heat from the solution, produces a refrigerating effect in the evaporator when cooling water is circulated through the condenser and absorber. The absorption cycle is energized by a heat medium (hot water) at 70-95°C and the condenser is water cooled through a cooling tower. When the heat medium inlet temperature exceeds 67.7°C, the solution pump forces dilute lithium bromide solution into the generator. The solution boils vigorously under a vacuum and droplets of concentrated solution are carried with refrigerant vapor to the primary separator. Subsequent to separation, refrigerant vapor flows to the condenser and concentrated solution is pre-cooled in the heat exchanger prior flowing to the absorber. In the condenser, refrigerant vapor is condensed on the surface of the cooling coil and latent heat, removed by the cooling water, is rejected to a cooling tower. Refrigerant liquid accumulates in the condenser and then passes through an orifice into the evaporator. In the evaporator, the refrigerant liquid is exposed to a substantially deeper vacuum than in the condenser due to the influence of the absorber. As refrigerant liquid flows over the surface of the evaporator coil it boils and removes heat, equivalent to the latent heat of the refrigerant, from the chilled water circuit. The recirculation chilled water is cooled to 7°C, and the refrigerant vapor is attracted to the absorber. A deep vacuum in the absorber is maintained by the affinity of the concentrated solution from the generator with the refrigerant vapor formed in the evaporator. The refrigerant vapor is absorbed by the concentrated lithium bromide solution flowing across the surface of the absorber coil. Heat of condensation and dilution are removed by the cooling water and rejected to a cooling tower. The resulting dilute solution is preheated in a heat exchanger prior returning to the generator where the cycle is repeated (for details, see Yazaki Energy Systems, 2008).

Fig. 7.3 An ACS considered for the building in Bigadic (Yazaki Energy Systems, 2008).

7.3.3. Model building

The wall structures may vary from one region to another. The materials used in the construction of buildings consist of stones, concrete, bricks, and reinforcement iron bars. In Bigadic, brick walls, and polystyrene of 2 cm thickness is commonly used as an insulation material. Table 7.1 gives commonly used wall structure for buildings in Balikesir and its thermal characteristics, including the conductance U-value, thermal resistance, heat gain, and infiltration information. In calculations, U, A, and UA are used as the heat transfer coefficient, heat transfer area, and overall heat transfer coefficient, respectively. Method simulates building and equipment Chosen absorption system utilizes a solution of lithium bromide and water.

Table 7.1 Some data and properties of the model dwelling._

Table 7.1 Some data and properties of the model dwelling._

Outside wall

96 24

0.52 2.70

49.92 64.8

(20 cm hallow brick + 2 cm insulation) Double-wane windows


(with 8 cm insulation)

Total UA (W/°C)

38 152.72

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