Cool Roof Calculator
Web address: http://coolroof.cbs.iiit.ac.in/
A roof that reflects and emits the solar radiation back to the sky rather than transferring it into the building is termed as cool roof (Cool Roof Rating Council, 2013). Cool roof helps in reducing air-conditioning energy consumption in a conditioned building and improves thermal comfort in an un-conditioned building.
A tool has been developed that works on EnergyPlus and does online simulations for
Indian cities for which weather data files are available.
Compared to the other tools the Cool Roof Calculator provides more input details about the building and also detailed set of results including comfort. One other advantage of the Cool Roof Calculator over the other tools is that it has the capability of simulating an un-conditioned building for which the comfort achieved through the use of cool roof will be reported. Therefore, some of the major differences of the Cool Roof Calculator compared to other calculators are the features listed below:
- Performs online simulation
- Works on EnergyPlus engine
- Capable of modelling a un-conditioned space
- Generates thermal comfort results
- Does payback analysis
- Works for all major Indian cities
The tool is developed on Apache/2.2.16 (UNIX). Web pages are developed in PHP and use Ajax Technologies. At the back end, socket programming has been implemented, the code for which is written in C. The inputs submitted from the User Interface (UI) are posted to a PHP script for simple or detailed case, which generates the corresponding EnergyPlus Input Data File (IDF) for both normal and cool roof simulation. The IDF name and the weather file name are then sent to an executable waiting for a socket connection (to open). The executable then calls a bash script which performs the simulations while the front end shows the simulation progress. Once the simulations are done, the UI is redirected to the results page which shows the results.
The calculator can model several combinations of the building type, location, material type, HVAC type and so on leading to millions of combinations.
There are four kinds of building types considered in the calculator – Office, Institute, Retail, and Residential.
There are four different types of Heating Ventilation and Air-conditioning (HVAC) systems are available for selection – Packaged Terminal Heat Pump (PTHP), Packaged Single Zone (PSZ)-HP, Central Air conditioner with water cooled chiller, and Central Air conditioner with air cooled chiller.
It is practically not possible to generate models for all these combinations and check them for accuracy. One simple model is simulated with all HVAC system types and weather data is selected for New Delhi climate.
Here are some of the results of different models:
1)Simulation result for simple office model:
2)Simulation result for simple institute model:
3)Simulation result for simple retail model:
4) Unconditioned Residential Type:
There is no apparent effect on energy savings by cool roof for unconditioned buildings but cool roof is capable of increasing the comfort condition inside buildings. So to demonstrate the effect, the monthly Mean Air Temperature for cool roof and dark roof is shown for all months.
The figure below shows the change in Fanger PMV with application of cool roof. Reduction in Fanger PMV in the range of 0.6 to 1.6 has been observed.
The calculator provides parametric simulation results for different insulation thickness with and without cool roof. User can select insulation thickness from the curve. The calculator also provides a graph between roof insulation and energy savings from cool roof over normal roof.
The current version has been tested for stability and compatibility. Cool roof calculator is able to handle the load and no crash has been observed.