4.7 Initial Input Data for Simulation Process
4.7.3 The Initial Conditions for the Indoor Thermal Performance Simulation Software
162 The microclimate parameters average values of these receptors will be plotted and discussed.
Moreover, the average values for the output data will be integrated to the IES-VE as an input external microclimate conditions.
Figure 4.21: The selected height of 1.4m from the ground the for the extracted outdoor micro climate data (Author, 2018)
4.7.3 The Initial Conditions for the Indoor Thermal Performance Simulation Software IES-VE
163 The solar gain covers the external and internal heat gains, the external solar gain reflects the effect of the exposure to the solar radiation of the sun, and the internal gain covers a number of variables and initial conditions that will be set in the IES-VE software prior to running the simulation process. The internal gain input data will be the same for the base case and all configurations. Hence, the variation in the output data of the solar gain extracted from the IES-VE software will reflect the variation in shading effect and external gain occurred by the variation in buildings height and configurations within the group. On the other hand, and as illustrated previously in literature review chapter, the cooling load includes the cooling sensible load and the cooling latent load. The cooling sensible load reflects and affected by the dry bulb temperature, whereas the cooling latent load depends on the wet bulb temperature. Therefore, the maximum dry bulb air temperature and the wet bulb air temperature extracted for the ENVI-Met simulation results will be the input micro climate data for the external heat gain in the IES-VE simulation process. Figure 4.22 illustrates the base case (G + 5) of the urban block presentation in the IES-VE software.
Figure 4.22: The base case configuration (G + 5) of the urban block presentation in the IES-VE (Author, 2018)
164 4.7.3.1 General Input Data for Indoor Thermal Performance Prediction Software IES-VE
The energy consumption of the residential buildings in hot climate is mainly dominated by the cooling load consumption. In this study location which categorised as a hot desert climate zone, buildings cooling strategies depends mainly on mechanical system which may be used continuously most days of the year. Therefore, the cooling plant load is selected to explore the effect of urban topology on energy consumption of the residential buildings. For this study, the cooling plant load is going to be estimated using the IES-VE software, and it will be designed to maintain an indoor air temperature of 23ᵒC. The IES-VE simulation software offers a wide range of indoor environmental a thermal parameters with respect to building envelop and materials. In addition of taking the building operation and the occupation effect in to consideration, furthermore, the IES-VE offers a very good level of accuracy.
The input data required to run the IES-VE simulation process is divided into types; 1) the model physical data, and 2) thermal initial data. The model physical data covers the model dimensions and specifications including the building materials. The model of the base case and the proposed scenarios will be modelled in the IES-VE working space with all exact dimensions implemented in using the ENVI-Met software. With respect to the physical dimensions of the model, no variation occurred in the modelling procedure between the two software, the dimensions, coordinates and the cell size (scale) used is the same in both ENVI-Met and IES-VE software. The IES-VE provides a larger number of built-in weather file depending on the location of the earth, this weather file covers countries from all contents. The nearest built -in weather file to the location of this study is the same weather station data used to collect the average of micro climate data for ENVI-Met data input Dubai International Airport Station. However, the build-in weather file in the IES-VE does not allow to calculate any variation in the outdoor microclimate conditions caused by the effect of buildings topology.
165 Therefore, the outdoor microclimate data of the investigated models will be extracted from the ENVI- Met software and will be used for running the IES-VE software. One of the IES-VE limitation mentioned in the methodology chapter, is the limitation of the microclimate condition that can be inserted in the IES-VE.
The IES-VE allows editing of the design air temperature, dry bulb and wet bulb only, any variation in wind speed could not been added to the IES-VE weather files. On the other hand, the ENVI-Met software is well known in conducting the CFD simulation, therefore, the maximum air temperature extracted from the ENVI-Met is normally affected by the variation in wind speed. Furthermore, the data of the relative humidity extracted from the ENVI-Met is in the percentages.
The wet bulb air temperature was calculated using an application that calculates the wet bulb temperature using the dry bulb temperature and relative humidity. However, building materials and specifications will be indicated using Building Manager prior to running simulation process. The default file for building material covering walls, roofs, facade material can be used to indicate the required material specifications for the simulated models.
The built-in specification and thermal conditions follows the ASHRAE load requirements.
However, and with respect to the 'Sa'fat', the Dubai Green Building Evaluation System, the U- Value for the external wall is varied between 0.57 W/m² k for bronze and silver
'Sa'fat', and 0.42W/m² k for the golden and platinum 'Sa'fat', and for the roof the U-Value is 0.3 W/m² k. The buildings material specifications and the typical construction setting data for
the simulated models is illustrated in detail in appendix B. Furthermore, and with respect to the indoor conditioning system setting conditions, the acceptable indoor air temperature for the hot desert climate is varied between 23 ͦ C and 25 ͦ C (Al-ajmi and Loveday, 2010).
Moreover, building operation and occupation data should also be set prior to simulation
166 process. New thermal profile has been set in the Building Manager, this file contains the operation and thermal input data as illustrated in table 4.2.
The air temperature is set according to the default temperature suggested by the IES-VE according to the location to be 23 ͦ C. Moreover, and according to ASHRAE (2007) the ventilation rate is generally varied between 1 for low contaminate air to 4 for high contaminate air, gasses and dangerous particles. In order to achieve an equilibrium pressure, the amount of the air leaving the space and entering the space must be the same, and the ventilation rate is set for the low contaminate air to be 1 ach (air change per hour). The actual amount of air change in a well mixed ventilation scenario will be 63.2 % after 1 hour and 1 ach ( Bearg 1993). With respect to the urban block floor layout, number of apartments and occupants or people calculations. Each floor area is 900 m² , and it is consist of apartments with 180 m² floor area and two bedrooms. This result in 5 apartments in each floor, for the ground floor the number of apartments is 4 as the ground floor contains of some services and reception area.
According to ASHRAE (2009c) the calculation of the people number in the residence unit is the bedroom number plus one.
The calculation will be based on the base case block of 24 buildings (G +5) as the following:
Ground Floor = 4 apartments * 3 people = 12 people
Typical floor = 5 apartments * 3 people = 15 * 5 floors = 75 people Total number of people in each building = 87
Total number of people in the urban block = 2,088
The number of 2000 people will be used for the proposed urban block residents
167 Table 4.2: The setting conditions in the typical thermal file in the IES-VE software for all
configurations
--- [LOCATION] --- The Location on earth: Longitude55°.33' ;Latitude 25ᵒ.25' Weather station: Dubai International Airport Station Loads methodology: ASHRAE Loads [THERMAL CONDITIONS] --- Project daily profile: Continuously Project weekly profile: Continuously System to maintain cooling at: 23 ͦC The internal gain -florescent type consumption: 10 w/m² The number of occupancy: 2000 people The natural ventilation maximum flow: 1 ach Maximum dry bulb temperature: Varied according to each configuration Minimum dry bulb temperature: Varied according to each configuration Wet bulb temperature at maximum dry bulb temperature: Varied and extracted from the relative humidity of each configuration
Chapter 5
The Outdoor Thermal Performance of the Proposed
Configurations
169