Energy Modelling: Balancing Performance and Costs

Engaging an energy modeler that understands all relevant components of building development can add significant value for projects. Early inclusion of such an energy modeler in the design team has the greatest potential to reap the possible benefits. In short, these benefits come in the form of cost savings for the building developer.

Maximizing the Benefit of an Energy Modeler

In many cases, the primary reason for a building developer to engage an energy modeler is to demonstrate code compliance. Code compliance means that the proposed building meets the requirements of the relevant building code (this article focuses on the energy efficiency requirements). However, a building developer should view an energy modeler as a team member that adds value, outside of their intended primary function. There are many design decisions which an energy modeler can inform while ensuring the building remains code compliant.

Assuming the energy modeler is engaged after site location and the building orientation, footprint and layout are already selected. They are ideally placed to inform the next steps of architectural, electrical and mechanical design. The first step is for the energy modeler to gather relevant information from the design team and understand the preferred design components. However, the design team may need to compromise on certain components to achieve code compliance.

Building Component Selection

Balancing the selection of building components, which impact building energy performance, and the cost to the project is a vital role the energy modeler can fulfill. This role provides a significant value add by minimizing the cost of the project while ensuring design meets energy code requirements. Building energy performance and related code compliance are impacted by a variety of building component selection decisions. These components include, but are not limited to:       

Detailed energy modelling allows for a variety of scenarios to be examined. In each scenario, the selection and combination of building components is varied. The selection of building components is influenced by the design team’s input and complemented by the energy modeler’s knowledge of how each component influences building energy performance.

Giving the Developer Options  

The energy modeler can present various design options to the developer and wider project team. Subsequently, feedback from the design team can narrow down the design details. Finally, the energy modelers can run further iterations to ensure the most favorable design is selected.

For simplicity, assume that for each building component, increased costs lead to increased energy performance. The energy modeler best understands how each component influences the performance. On the other hand, the developer best understands the cost to the project for each component. Combining these two knowledge bases allows for the greatest value for money in relation to building energy performance. Consequently, the building developer can achieve cost savings. Savings are achieved by avoiding excess costs to the project on building components which do not have a justifiable impact on the building performance. Conversely, the project can benefit from cost-effective design components that achieve the required building performance.

Choosing the Optimum Design

This transparent, interactive process between the energy modeler and the design team allows for an optimally designed building. As a result, the project team are best aligned to make smart decisions and achieve the required code compliance. These decisions should balance energy performance and project costs.   

To maximize the added value previously described, it is beneficial to engage an independent energy modeler. A significant portion of projects hire energy modelers on projects from consultants already providing other design services on that same project. Unfortunately, this approach can reduce the potential benefit of the energy modeler by introducing a bias towards certain design solutions. For example, mechanical consultants may favor a design that relies heavily on certain mechanical systems, while building envelope consultants may prefer increased envelope performance solutions. While both approaches may achieve the required result of complying with code, this can result in costly solutions and sub optimal building performance.

Therefore, independence and non-bias are important criterion for a project’s energy modeler. It is difficult to optimally serve a developer’s interests while providing design services on the same project. It is best that the energy modeler acts solely as the developer’s energy and sustainability representative. In this case, the building developer can realize cost savings and ensure code compliance.

Definitions and Acronyms

• HVAC – Heating, ventilation and air conditioning – Desired internal conditions are maintained by the mechanical components that make up the HVAC system.
• LPD – Lighting power densities – The total power of installed lighting fixtures per unit of internal floor area.
• R-value – A measure of how well a building element resists heat flow. The higher the R-value, the more resistance to heat flow the element provides [1].
• U-value – Overall heat transfer coefficient. Describes how well a building construction element conducts heat. A U-value is a sum of the thermal resistances of the layers that make up an entire building element [2]. It also includes adjustments for any fixings or air gaps. It is the inverse of the aforementioned R-value. To clarify, a lower U-value indicates higher insulating properties. 
• SHGC – Solar Heat Gain Coefficient is the fraction of incident solar radiation that a window admits. The SHGC is a number between 0 and 1. A lower SHGC indicates a lower solar gain through the window [3].
• HRV – A Heat Recovery Ventilation (HRV) is a system that uses the heat in stale exhaust air to preheat incoming fresh air. This reduces the energy required to bring outside air up to ambient room temperature so saves money on heating bills [4].

References