In the simplest terms, an energy model is a set of computer-generated calculations that provides information predicting anticipated energy consumption of a building and its systems. An energy model is a ‘whole building energy simulation’. You could consider it, along with all forecasting computer models, a time machine that provides us a glimpse into a probable future.
Imagine that you’ve hired architects and a set of engineers to design a new 6-story office building that will have an upscale restaurant on the first floor. As the owner, would it be important for you to know what your energy bill will look like every month? Of course it would! Knowing how much you’ll have to spend on energy, along with numerous other operational costs, is essential in determining economic viability and profitability for the building.
As a Design Tool – Minimizing Risk
An energy model would be a vital tool to help you and your designers understand how the building uses energy. It will tell you how much electricity the building’s lighting, air conditioning, and heating might use. It can tell you how much natural gas the restaurant’s commercial equipment might use. The key purpose of the information gathered from an energy model is to assist you and your designers in making informed decisions for every part of the building that will impact energy consumption. An energy model helps an owner reduce risk of uniformed design decisions that can lead to failed or over priced systems.
An energy model is a time machine of sorts. It allows you to glimpse into a probable future. Wouldn’t you think that if a time machine were available, everyone would use it when they’re designing a new hospital, bank, shopping mall, office, or home? The answer is, unfortunately,no. The vast majority of owners and designers don’t take advantage of energy models. When energy models are created, they are mostly used as a verification document to meet imposed energy performance mandates or incentives that are usually governmental. They are used in the same manner for various performance green building certifications. For LEED certification a ‘whole building energy simulation’ is one of three options to verify anticipated energy consumption, the energy model being the option that can achieve the most credit points towards certification. Unfortunately, energy models are oftentimes not used for their primary purpose and the reason they exist in the first place.
The primary intended purpose of an energy model is used to provide a design tool and risk minimizer. Owners and designers can compare first cost, return on investment, and lifecycle costs among a plethora of building system elements, their interrelationships and relationship to energy. Energy models compare a typical building to the design of the new (or completely renovated) building. It is this comparison that assists design teams in making choices and in turn lowers risk. Energy models help to answer big questions: 1) Will the new building cost more, less, or the same as a comparative building and why? 2) How can we reduce cost and improve performance? 3) Should we install an air or water-cooled mechanical system? 4) Does it make economic sense to install a ground-source-heat-pump?
The detailed data input to energy modeling software includes the building’s location, orientation, windows, roof, insulation, heating, ventilation, air conditioning, lighting, and controls. Data about the building’s proposed hot water generation and distribution and whether there will be photovoltaics (renewable electricity generated from solar panels on site) is part of the data that energy modeling software processes.
Architects and engineers can choose the optimum position of the building’s relationship to the sun minimizing energy for cooling. They can determine whether using a highly reflective window is wasting money when a moderately reflective window will work just as well. The owner can understand the difference between the proposed installation of a 20,000 watt or a 50,000 watt solar electric system and determine how long it will take to pay for it and decide which system is best. Energy models help owners and designers decide on the best color for the roof–spray-foam or fiberglass insulation is best, and whether more insulation can lower the cooling capacity needed air conditioning, which will result in lower equipment costs. All of this can only be done if energy models are used early in the design process. If they are created only to report on expected energy consumption, they are not used as intended. Without using an energy model, the office building with the restaurant will be designed with guesswork and anecdotal experience, significantly increasing the risk of poor performance, higher operational costs, and dissatisfied occupants.
Energy Model Accuracy
Armed with this powerful tool, designers are able to make choices that improve performance, reduce costs for installed systems, and reduce electric and gas utility costs throughout the building’s life while reducing greenhouse gas emissions.
Why isn’t it standard practice to use energy models when designing any building? The biggest reason is the lack of understanding of their benefits. The belief is that energy models cost too much, take too much time to create, and aren’t accurate. There is no question that energy models cost thousands of dollars and take days and sometimes weeks to develop. When, however, this ‘first cost is factored into overall design, its benefits of risk management and specifying efficient systems more than pays for itself.
As for accuracy, energy modeling is an art. It takes a creative, refined, intuitive, experienced, energy-modeling expert to create and use the modeling software to deliver the accuracy. Energy models with their creators simulate a building’s projected energy performance. No one can model actual future use or events. There is a multitude of real-life variables that impact a building’s energy use and consumption. There have been a lot of misconceptions about model accuracy. First of all, no one can verify model accuracy until the building has been in use for at least 12 months, and 24 months’ usage is best to access accuracy. Many believe that the model and real-life use should be within a percentage point. That can be true so long as all systems have been designed, installed, and are operated in line with the data given to and input by a modeling artisan. The biggest reason noticeable differences are reported between the model and real-life consumption falls squarely on how the systems are operated. Without proper usage training of the complex, sophisticated installed equipment, operations personnel are often responsible for managing systems improperly, which in turn dramatically effects energy consumption. There are many factors an energy model may project consumption inaccurately. With a skilled modeling artisan, however, proper robust data input, and proper use of the model as a tool for design, accuracy has been reported to be spot-on for the vast majority of the time.
In short, an owner of any type of building should spend the time and money to create an energy model and use it as a design tool as intended. Energy models pay for themselves within months, and need to be part of the architects’ and engineers’ toolkit. Energy models are essential in increasing building performance and owner/occupant satisfaction while minimizing risk and reducing greenhouse gas emissions.