Multifamily New Construction: Is air-source the solution to electrification of apartments? VRF vs. PTHP - by Jamie Fales

When choosing between Variable Refrigerant Flow (VRF) technology and Packaged Terminal Heat Pumps (PTHPs) for new construction buildings, it’s important to be aware of the key differences in installation and maintenance. Exploring factors like equipment setup, testing, air sealing, and efficiency helps building managers make informed decisions to improve comfort, reduce costs, and optimize performance.

Installation:

• Outdoor Equipment:

- VRF Systems: present challenges in installation and maintenance due to their complexity. VRF systems require meticulous pressure testing, evacuation, and refrigerant charging for each unit. Outdoor units are large and heavy and will likely need a crane to be set on the roof.

- Air Source PTHPs: Heating and cooling provided through the wall of the apartment. Once a penetration is made though the façade and waterproofed properly, exterior work is completed.

• Indoor Equipment:

- Both systems hung, powered, connected to a thermostat and condensate drain line.

• Commissioning Testing:

- Outdoor VRF Equipment: In larger buildings, outdoor VRF units are needed for each line or floor, necessitating complex refrigerant line installations and extensive testing for leaks and pressure maintenance. Pressurization, evacuation, and refrigerant charging often require multiple days per unit for completion and will require coordination of each with the installer, commissioning agent, and factory authorized technician, adding labor, expense, and time. Documentation is needed to confirm proper procedures are used, to avoid mistakes such as water in the refrigerant lines and improper amount of charge for system requirements.

- Indoor Equipment (Same for VRF and PTHP): Involves testing around 10% of apartments, ensuring they function correctly. Equipment is tested to confirm operability in heating and cooling modes, proper placement and readings of the thermostat, and that filters are installed (and clean prior to occupancy).

• Air Sealing:

- VRF: Few façade penetrations for the refrigerant piping, all near the outdoor VRF equipment.

- PTHP: Penetrations at each unit. Traditional large openings in the façade similar size to PTACs can create a lot of difficulty meeting air sealing requirements. Some newer systems use two small tubes to pull air from outside to be used to move heat, the small tubes (think two 3-4” tubes per unit) can be well sealed between inside and outside.

Operation and Maintenance:

• Tenant Comfort:

- Typical 2-pipe VRF: System may have delays in providing heating or cooling during marginal temperatures (spring/fall 50°F to 75°F outdoor temperatures) as the system will work to satisfy whatever operation call (heating or cooling) is present before switching over to satisfy the less popular call.

- PTHP and VRF with Heat Recovery: From the perspective of the end user, there’s no discernible difference in the comfort experience between a PTHP and a heat-recovery VRF. Tenants have heating when needed and cooling when desired.

• Cold Weather:

- All Air-Source Heat Pumps may struggle to operate efficiently in extremely low exterior temperatures, necessitating the use of electric resistance heaters, which are less energy-efficient. Technology has improved significantly in the last decade, heat pump operation on the coldest New York Design Days now can continue without need for electric resistance.

• Servicing:

- VRF: Error codes generated in one terminal unit may cause a whole line to stop operating until a service contractor can be on site.

- PTHPs: Equipment can be swapped out with one visit to a tenant apartment, equipment can be serviced by site staff or sent out for repair.

• Future Proofing:

- VRF: There’s a risk of future compatibility issues if manufacturers discontinue products or technological advancements make current systems obsolete. Manufacturers may have different requirements for refrigerant connections requiring refrigerant line replacement, locking a building in to one manufacturer’s equipment.

- PTHPs: Each unit operates independently. If a piece of equipment breaks and cannot be replaced in-kind, the replacement unit only needs to be sized appropriately and fit in the same sleeve.

• Billing:

- VRF: Operating expenses are split between the house meter and tenant meters as outdoor equipment is powered on the house meter. Manufacturers often have a way to allocate usage to individual tenants and can create a billing invoice.

- PTHPs: All operating expenses occur on the tenant meter as all equipment is in the apartment. This may result in increased utility allowances for buildings required to pay tenant heating.

The installation and maintenance of HVAC systems play a pivotal role in ensuring occupant comfort and building efficiency. While VRF technology may offer increased energy savings, it also presents unique challenges in installation complexity and commissioning testing. PTHPs, on the other hand, provide simpler setups but may lack the efficiency of VRF systems. Developers and building managers must carefully weigh the pros and cons of each system to determine the most suitable solution for their specific needs. By understanding the nuances of installation, operation, and maintenance, you can effectively select HVAC systems to reduce installation costs, construction timelines, optimize performance and maintain tenant comfort, all while meeting your carbon footprint goals.

Jamie Fales, CBCP, is Director of Commissioning at KOW Building Consultants, Manhattan, N.Y.