Is Operative Temperature Control in early Design Stage Tools a reasonable Trade-off between Precision and Usability?

Using hourly thermal simulation tools in the design stage effectively assesses the potential consequences of design options on a building’s thermal performance. Over 300 tools are available for such simulations. Advanced tools offer high modeling options and predictive precision but require many inputs, expert knowledge, and long simulation times. Conversely, some tools are developed to increase usability and reduce calculation time, though they come with less precision and fewer modeling options. These simplified tools are typically used in the early stages of the design process.

Several studies have identified desirable features for these programs: easy-to-use, fast, and ‘precise enough’ are often emphasized when developing simplified thermal performance simulation tools for design practice. Recently, it has been realized that successful implementation of such tools requires fitting them to design activities rather than making workflows fit the input flow of a simulation tool.

Developing tools that are easy-to-use, fast, and ‘precise enough’ presents many challenges. This paper analyzes an approach used in simplified thermal simulation tools, specifically operating systems with respect to operative temperature rather than air temperature. This approach’s advantage is that it simplifies obtaining results that comply with international standards for the thermal indoor environment, which sets criteria for operative temperature. However, in practice, systems are rarely controlled with respect to operative temperature but rather air temperature. Setting an appropriate air temperature setpoint in a tool to make performance simulations comply with operative temperature requirements can be tedious and must consider energy performance requirements.

The BESTest framework was applied to investigate the precision of an existing, decade-old tool designed for early-stage building design that uses operative temperature for system control. The benchmark results in BESTest are from models using air temperature for control, but the tool performs within many BESTest bounds. Further analysis indicates that full compliance could be achieved if the tool used air temperature for control instead. Therefore, using operative temperature for system control in early design stage tools may be a reasonable trade-off between precision and usability.