Bi-directional Flow of Information
Energy modeling as a tool in a RCx project is very effective because the energy model supplies information to the RCx project, and the RCx project feeds information into the energy model. This perpetual flow of information leads to snowballing insight. Cause and effects become more clear, and the intertwining nature of building operations becomes evident— and better understood.
RCx Information Flowing to the Energy Model
The process of developing the energy model inputs can be much less intimidating in a RCx project. Questions about the building envelope, equipment capacity, motor sizes, room-usage patterns, lighting and other things are easily answered: Simply go look at the building!
However, the less obvious observations from the RCx process are key components of information that can enhance the energy model. Results from functional testing can be added directly to the energy model. Find a VAV (variable air volume) damper that’s stuck wide open? Is there an air handler that never reaches its static pressure setpoint? Discover lights are left on overnight? These observations can all be directly input into the model; information flows from the RCx project to the energy model.
The utility usage data reviewed in an RCx project also flows into the energy model. Actual usage can be compared to the model’s usage. This can then be used to guide tweaks to the model, and the model’s energy use can be calibrated to that of the actual building.
It is important to note that reflecting actual energy use was never the intent of an energy model. The process is often difficult and time consuming. The payoff is a high degree of confidence in the model (and any savings calculations evaluated by the model) and, oftentimes, additional insight into the building’s performance (information flowing from the energy model to the RCx project).
Energy Model Information Flowing into the RCx Project
The value of a RCx project is that the results will help to guide decisions made by the owner. The energy model can play a role in supplementing other RCx observations to further assist the owner with his or her decision-making.
The energy model calculates energy savings while accounting for all interactions between systems. An example that illustrates this is the evaluation of a lighting replacement project. If the RCx observations note a building has legacy fluorescent lighting and a recommendation is to replace the lighting with LED lights, the energy model will calculate the electrical savings at the lights, as well as the effect it has on the HVAC system. This means you can also quantify—with a high degree of confidence—the change in heating and cooling loads this change would have. Information, such as peak-load reductions and even cooling-tower water temperature bins, can be provided as part of the RCx report, thanks to the energy model. System interactions become clear and quantifiable with help from the energy model.
The load information provided by the energy model can also be used to evaluate sizing of equipment as part of the RCx project. It’s possible to go beyond rules of thumb and experience and confirm sizing issues with hard data.
The owner then can make more well-guided decisions with this additional information.