Synopsis

This tutorial explains how to use Ecotect to generate and interpret results for a hourly heat gain/loss graph.

Duration

You will need about 15 minutes to complete this tutorial.

Training and Accreditation

Successfully completing this tutorial fulfills one of the practical skills required for completing Level 1 of the Thermal Performance training module.

Resources Required

To complete this tutorial, you will need the SimpleThermalModel.eco file located in the Examples folder of your Ecotect installation.

Tutorial

Calculating the Graph

1. Open the SimpleThermalModel.eco file in Ecotect. The model consists of three simple zones with various window openings. Go to the Calculate»Thermal Analysis... menu item. The Thermal Analysis calculation wizard appears. Choose the Losses and Gains radio option and the click Next.
   

   Start the Thermal Analysis wizard, and select Losses and Gains.
2. On the next screen of the wizard, select the Hourly Losses and Gains radio option. The other options allow you to select other ways of displaying gains (covered in other tutorials). Click Next.
   

   Select Hourly Losses and Gains, and then click Next.
3. Select the day that you wish to calculate hourly temperatures for. You can do this manually, or click the Search Weather Data button to use pre-defined days, such as Hottest Day (Average) (if you haven't already set the location for your project, you will be prompted to load climate data before this context menu appears). Important Note: the orientation of your model will also effect the results of the hourly temperature graph, so make sure you have the correct north orientation for your project before proceeding.
   

   Choose the day/s to calculate.
4. Click Ok to calculate the hourly heat gain/loss graph, similar to the following screenshot (you may be prompted to recalculate interzonal adjacencies first - click Yes).
   

   The Hourly Losses and Gains graph.

Interpreting the results

Let's now have a look at the legend in order to interpret the results.

1. 
   The bright green line represents the HVAC load, which is the amount of energy that would be required to maintain the zones at a comfortable internal temperature. As we don't have any air-conditioned spaces within this model, the HVAC load displays as zero.
2. 
   The solid red line represents conduction - gains/losses that occur through the fabric of the building itself. The materials you select for the construction of the building envelope with affect gains and losses due to conduction.
3. 
   The dashed red line represents gains due to indirect solar exposure, otherwise known as the Sol-Air temperature. These heat gains are caused by the molecular excitation within the building materials when exposed to solar radiation.
4. 
   The orange line refers to direct solar heat gains. These gains occur through transparent surfaces such as windows and skylights (whereas Sol-Air refers to gains via opaque surfaces, so hence are indirect solar gains).
5. 
   The dark green line represents gains and losses that occur due to ventilation and infiltration. In Ecotect, the opening/closing of windows and other ventilation openings can be controlled via an operational schedule, while the rate of infiltration is set under the Zone Management control panel for each zone.
6. 
   The blue line represents internal gains due to artificial lighting, occupancy by people and equipment. Internal gains and occupancy rates can be set via the Zone Management control panel for each zone, while objects such as appliances can be assigned heat output values in the material editor.
7. 
   Lastly, the cyan line represents gains and losses that occur between adjacent zones. Note that this calculation only includes zones marked as thermal.
8. 
   If you select a specific zone via the Highlight Zone drop-down list below the graph, this isolates the tabulated results shown right for the selected zones. Otherwise, leave this on All visible thermal zones.
   
   

Working with the results

In addition to simply comparing the magnitude of gains and losses between different configurations or design options, it is also important to be able to recognise patterns within the data that will let you relate back to the geometry and materiality of the model. This is best done through trial and error with your own models, however as an initial introduction some simple solar and thermal mass effects are illustrated.

1. Insulation : The R-value of a material indicates its resistance to heat flow. Try changing the roof material from Clay Tiled Roof to a more insulated material such as Metal Deck Insulated, and then recalculate the graph. Note that there is a significant reduction in conduction gains by choosing materials with a high R-Value.
   

   Conduction Gains are less with a more insulated roof.
2. Thermal Mass : The external walls of the thermal zones in this model have been assigned the Brick Timber Frame material. Try changing these walls to a construction with greater thermal mass, such as Rammed Earth 500mm, and then recalculate the graph. Note that there is a reduction in conduction gains, as materials with a high level of thermal mass both reduce the overall amount of heat flow and delay it transmission from inside to outside.
   

   Add walls with more thermal mass as well, and temperature fluctuations even out due to transmission delays.
3. Solar Gains : The orientation of windows within a model will determine when in the day solar gains occur within a zone. Obviously east-facing windows will let in early morning radiation whilst west-facing windows will let in mid-late afternoon sun. For example, try deleting the west facing window, and then recalculate the graph.
   

   Deleting the west window reduces direct solar gains in the afternoon.

Conclusion

As you can see, factors such as material selection and window orientation can have a significant impact upon heat gains and losses within a building. Using Ecotect, it is possible to make informed decisions about these matters even at the schematic design stage of a project.