As you drive around many cities you may have noticed that multifamily projects are on the rise. While we are stoked to be riding this tidal wave of new multifamily construction, we are not new to the sport. Southern Energy Management’s first high performance multifamily project was certified over 10 years ago. Since then, we have been consulting, energy modeling, and testing buildings. We understand that multifamily buildings are complicated, and nothing is ‘typical’. They require special attention and that includes building systems such as HVAC. We are proud to partner with Shane Nault, President of Building EnergetiCx on this blog post to bring you seven details that will help your projects get the most from your HVAC systems.
As with any project, thinking about the HVAC systems should begin during the design phase. One component that is often overlooked is the building and unit air balance. It may seem simple to think the HVAC unit simply recirculates air within the individual unit; however, you would be missing some key elements. Building codes require both ventilation air and exhaust air for commercial projects. Exhaust air includes exhaust for the unit bathrooms, but the exhaust air for clothes dryers and kitchen hoods also needs to be considered. While these are intermittent in use, they can be an issue when the perfect (or not so perfect), situation comes up in which all three exhaust systems are running at the same time. This can pull unwanted, unconditioned, and unfiltered air into units that negatively contribute to energy use and may decrease air quality. This is where air balance comes in. The proper amount of ventilation and the proper amount of supply air needs to be removed/delivered to each zone to ensure uncontrolled air movement is minimized.
The typical HVAC system that is installed for multifamily projects is a split system heat pump / air conditioning unit. These split systems work, but they can create issues when the units are oversized for the space they are conditioning. If the units are oversized they will tend to short cycle (this means running for short periods of time due to a massive amount of conditioned air being delivered to a space), and not pull enough moisture out of the air during the cooling season. Many do not know that in addition to cooling the air, HVAC systems also dehumidify the air; the latter requiring the system to run for an adequate amount of time to be effective. This ‘short cycling’ can cause humidity issues in warm, humid climates. In recent years our team has seen an increase in VRF (Variable Refrigerant Flow) systems, which helps greatly with energy efficiency and better comfort control of the units.
In general, the HVAC equipment manufacturers shouldn’t matter too much. However, the design engineer who is approving the equipment submitted should pay close attention to the features and options of the systems to make sure they provide the proper functionality. In addition, the design engineer should always ensure that the system performance matches the selected equipment.
Air leaks in forced air duct systems, or duct leakage, can be a major source of energy waste and can create comfort issues. During our commissioning process we find that duct leakage often occurs in three main locations: where the duct connects to the air handling equipment, at the duct joints and connections, and at the discharge air openings. When installing ductwork, it is important to seal all the seams and connections. The best way to seal the ductwork is with duct mastic, another often used method is with foil tape.
When making field observations it is important to inspect the ductwork prior to insulation to ensure that seams and joints are sealed. Also check the connections to equipment, especially once the unit is operational. And finally check after the drywall is installed to confirm all duct openings are accounted for. On a recent project it was discovered that some of the supply registers in the room had been completely covered with drywall. In addition, it is important to check the air gap between the drywall and ductwork at the supply register openings as these should be sealed. We have observed leakage of up to 40 cfm (cubic feet per minute) per supply that was not sealed, and if your ducts are not located in conditioned space (often the case for top floor units), this is a big deal in the way of energy efficiency.
Commissioning is the process of verifying all or some (depending on scope) of the subsystems of a building post construction/renovation to achieve the owner’s project requirements as intended by the building owner and as designed by the architects and engineers. Often building commissioning is associated with commercial projects and not all multifamily projects are commercial. As you may have guessed, many multifamily projects are not commissioned. Not commissioning a building, no matter what type, does not make the problems go away. This only allows them to persist and potentially grow into larger issues.
During the commissioning process the most common issues we find are power related. Often at the end of a project the electrician has many things to complete and getting power to the HVAC equipment is key. Once the HVAC equipment has power it sets off a series of events such as system start-up, controls verification, and final operation. Another common problem is HVAC system filtration – both with temporary filters and final filters. Temporary filters should be used during construction if the units are operational. Those filters should be changed out with clean final filters when the project is turned over to ensure the occupants have clean air to breathe (construction gets quite messy).
Having the right partner on projects is the key to success of the commissioning process. Based on our experience, the two key partners that support commissioning on a project are the Owner and the Contractor. Having a building owner who prioritizes quality, reliability, and functionality for their building is a huge advantage to the commissioning process. Having a general contractor who understands commissioning and the value it brings to their team at the end of the process is a breath of fresh air. Your project will get the most out of the commissioning process when these team members goals are aligned.
We hope this gives you some ideas on how to optimize your multifamily projects’ HVAC systems. Let us know how we can help in the HVAC design, inspection, or testing of your next development!
Headquartered in Charlotte, North Carolina, Building EnergetiCx is an independent commissioning firm that has successfully served on over 170 projects, regionally, nationally, and internationally. The firm has quickly established an exceptional track record of commissioning and related energy consulting work since its founding in 2011 by President Shane Nault. To-date the firm has commissioned more than 6.9 million square feet of commercial, institutional or industrial space for facilities totaling more than $500 million in value.
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