We work on thousands of multifamily housing units every year providing certification, consulting, and testing services for affordable and market rate developers. Our influence tends to be somewhat limited as we do not have a financial stake in the projects, and we are only one of many project team members. The majority of our work is certification under the National Green Building Standard, EarthCraft, Enterprise Green Communities, LEED, and Green Globes.
Over the years we have worked steadily to improve the quality of design and construction on our clients’ projects. Some projects are receptive to our suggestions and invite us to participate in the design process. This allows us to help identify potential pitfalls and opportunities for improvement. In others, our suggestions are mostly ignored, and our work is limited to inspecting and providing certification. In that role, however, we still have some influence on the project, making sure insulation and air sealing are installed correctly, specifications are followed, and when testing is included in the work scope, that envelope, duct leakage, and ventilation flows meet targets.
While this does help improve the overall quality of construction, we see far too many missed opportunities where better decisions early on would have improved a building’s performance with little or no increase in cost. This is no more true than in the choice of HVAC equipment for these buildings.
King sized HVAC equipment, uncomfortable homes
The biggest challenge we find with multifamily projects is improving HVAC designs and equipment. Particularly in the Southeast where almost all apartments are conditioned with split system heat pumps. This equipment is typically located in a small mechanical closet with a lowboy electric tank water heater beneath it. The primary problem with these installations is the equipment sizing.
The smallest standard heat pumps available are a minimum of 18,000 Btuh, or 1.5 tons. These are typically 14 or 14.5 SEER, 8.2 HSPF, with single speed fans. Not terrible performance; Not much of a stretch over the building code either. The problem is that most of the units these heat pumps are installed in have loads in the range of 6,000 to 9,000 Btuh, providing far more capacity than required.
In warm and mixed-humid climates where air conditioning is used a large part of the year, this oversizing can create comfort issues as systems short cycle, limiting dehumidification. Occupants feeling clammy and uncomfortable will then set their thermostats to very low temperatures in order to lower the humidity. In particularly humid climates, some developers install in-wall dehumidifiers that help. However, they create a fair amount of heat that must be offset by additional cooling.
Lower capacity HVAC equipment is available with mini-split technology, both ducted and ductless, but adoption is still very limited in our southeastern market due to cost constraints (real or imagined) and fear of unfamiliar technology.
Ducts are overrated
Based on my personal experience with ductless mini-splits, I have talked clients ears off about the many benefits. Unfortunately, I’ve had no success getting anyone to adopt this technology in their projects. Tightly sealed, well insulated buildings can be conditioned well with a single ductless mini-split head, using small exhaust fans to transfer air into bedrooms as needed–my own house works this way.
Even when using a standard split system heat pump, it is very possible to reduce the duct runs, eliminating supplies at the perimeter walls and windows in favor of high sidewall registers facing towards the exterior. Compact designs can reduce ducts by 60% or more, lowering installation cost, with fewer opportunities for duct leakage.
On one recent project, during our initial review very early in the design process, the client and architect were receptive to alternative HVAC designs, including compact duct systems. Sadly, this information was not shared with the mechanical engineer who proceeded to prepare a standard layout with perhaps more ductwork than I had ever seen in a small apartment. Obviously cautious and risk averse, during a follow up call, the engineer stated that he designed what he was asked to design, the work was done, there would be no changes. This was followed by silence from the architect. The client was unfortunately unable to join the call and, as the project is already being priced by contractors, I have low expectations of anything changing.
“Value” engineering is part of the problem
Some of our clients use ductless equipment on projects, but it’s typically through the wall package terminal heat pumps (PTHP), the type of equipment used in many hotel rooms. So far most are unwilling to look at more efficient ductless alternatives. One project in the design phase, consisting primarily of studio apartments, is currently considering ductless mini-splits. While we are hoping that this will actually come to pass, I am not holding my breath.
I find it interesting that with all the apartments being built that none of the major equipment manufacturers have come up with smaller heat pumps. What is keeping them from producing 1 ton or smaller systems? Mini-split systems are some of the only equipment available below 1.5 tons. These systems tend to both be significantly more efficient and more expensive. Even when they are considered, they’re frequently value engineered out of the project in an effort to control costs. While we have low expectations, we hope that we will someday see improved HVAC systems on more of our projects and will continue to keep up the good fight until it happens.
-Carl Seville is a green builder, educator, and consultant on sustainability to the residential construction industry. After a 25-year career in the remodeling industry, he and a partner founded a company, SK Collaborative. Photos courtesy of the author.