Cooling loads estimation analysis
For simulating cooling load estimation our team is using Trace 3D Plus software from Trane Inc. A full version of TRACETM 3D Plus, which implements EnergyPlus, is used to conduct the HVAC
simulations. The software is capable of calculating HVAC cooling and heating loads as well as
conducting an hour-by-hour energy analysis.
Since TRACE 3D Plus is a relatively new software and has some inherent limitations.
• Currently, the flexibility to create non-standard wall constructions is limited. As such, we
used standard wall configurations for the analysis.
• Few variables that would be useful for describing the performance of the house are not
accessible on an hourly basis.
Since the competition site is in the suburbs of city, we used Dubai International Weather for Energy Calculation (IWEC) data for our calculations.
Calculations are conducted as 43°C outdoor dry bulb, and 25°C wet bulb
The occupancy and lighting are assumed as 2 persons and 300 Watts.
The HVAC system will be selected based on the energy consumption and efficiency analysis. The preliminary analysis reveal that variable refrigerant flow (VRF) technology is most suitable for our house size range. This system suits most with respect to space and energy savings. VRF system uses heat pumps to provide heating and cooling for indoor and outdoor units with no requirement of duct system. VRF system includes multiple indoor units utilized by a single outdoor condensing unit, either with a heat pump or heat recovery system. R410a will be used as refrigerant.
Since we are still analyzing and weighing the construction materials, the selection of HVAC equipment is pending. It will be included in next submission.
Using a thermal zoning system we will set each space as an independent zone. Each zone will have its own thermostat to control space comfort conditions.
The following two sample load calculations are made; the extreme reference case with bare concrete walls and roof. While a second load estimation is made with insulations included.
The total cooling load without insulation is found as 43.2kW (12.27 Tonnes), which is obviously very high. This load reduced to 21.16kW (06 tonnes) when insulation is included on roof and walls. ASHRAE 62.1 data (that calculates fresh air based on people as well as area) is considered for the load estimation. Similarly, load estimates are done for summer with outdoor dry bulb temperature above 43°C. That is why, the total load seems on the higher side even with insulation included. If required, revisions to current estimations can be made based on the Solar Decathlon Competition Calendar schedules.
The following graphs present load estimations made with insulation considered. As could be seen from these figures, major load contribution is coming from the building envelope that contributes around 74% of the total load. Similarly, out of the four main external contributors glazing contributes the most (53%). While within the house areas, living room being the largest is the major contributor. It is worth noting that we used 75/25 percent heat transfer areas for wall and glazing. Further simulations will be carried out with varying heat transfer areas, construction materials and outdoor conditions to finally reach the optimum energy efficient house.
Load contributions in the house
A load of 6 tonnes can be easily handled with one outdoor unit. So we plan to install one air-conditioning unit of the required tonnage either on the roof or on ground outside the house.