Multifamily residential buildings have multiple separate housing units within a building. The housing units can be side by side or stacked (high rise). The scale of the building means they are treated like commercial construction with multidisciplinary design teams, commercial contractors and large scale commercial HVAC systems.
Hi rise buildings are common in urban areas due to the cost of land. They often include multiuse spaces such as retail, daycare and nursery schools, and community services. These additional spaces add challenges to the HVAC design as their use, operating hours and owners/tenant is quite different.
Ownership can also impact the HVAC design. Owner occupied apartments such as condominiums tend to promote HVAC systems where the occupant has more control over the operating cost. It is not unusual to see separate apartment power metering. Decentralized solutions such as Water Source heatpumps (WSHP) allow the occupant to manage their own maintenance and energy costs.
Rental units including low income housing can drive a different set of requirements. The building owner is more directly impacted by the energy and maintenance costs of the HVAC system so will likely want control. Access to apartments for service requires special planning and may include the need for security personnel. This can tend to promote HVAC systems that can be accessed outside the tenant space such as chillers/boiler with 4 pipe fancoils and a centralized ventilation system.
Hi-rise multifamily buildings will have more stringent design and construction requirements than single-family dwellings especially in the area of fire safety. Apartment units will be firewalled from each other.
So wall penetrations may be limited to 20 inches² before fire dampers are required. (check your local codes as this is not a universal requirement). Stack effect (movement of air in and out of tall buildings due to buoyancy) can also be an issue.
The occupant expectation is individual climate control so the HVAC system must allow for this. Commercial building automation systems (BAS) are not common in multifamily residential housing units. The occupant wants space temperature control and the controls must be easy to use by family members.
Energy Use in Multifamily Residential Buildings
- Pumps & Aux
- Pumps & Aux
Generally cooling loads are lower than other commercial spaces. The cooling load is more directly impacted by ambient conditions that internal heat gains. Building envelope (particularly glass) can have a major impact on overall cooling (and heating) loads. In temperate climate zones heating can be a dominant load. In cold weather climates, heating systems can be a life safety issue. Humidity builds up in cold weather climates especially in high-performance buildings that will require special consideration. In hot climates, dehumidification can be a challenge.
Ventilation requirements are covered in ASHRAE Standard 62.1 – Ventilation for Acceptable Indoor Air Quality. Local codes may have further requirements. While the ventilation rate (cfm/ft²) may be lower than other commercial spaces the ventilation air conditioning load can be a significant portion of the building energy load. Energy codes such as ASHRAE Standard 90.1 – Energy Standard for Buildings Except Low-Rise Residential Buildings often require air to air energy recovery for ventilation systems.
Domestic hot water loads are much higher in multifamily residential buildings than other commercial spaces and require special consideration.
Multi-use buildings add additional HVAC challenges. For example, a daycare or nursery space would require much higher ventilation rates and the load profile would be significantly out of phase (middle of the day vs. evening loads for residential) from the apartment units.
Multifamily residential buildings often show leadership in energy-efficient and zero-carbon design. For buildings owned by the public sector (affordable housing), the owner has a long term point of view and it is a method where the government can influence the market through leadership. In the private sector, there is a value proposition for high energy performance “green” buildings that resonates with a certain clientele.
As a result many cities and states have programs specifically targeted at multifamily residential buildings. These are often supported by incentive programs from the municipalities and local utilities. Programs such as Passive House are often cited as a compliance path for these programs.
The nature of individual housing units assembled together promotes decentralized HVAC systems. Decentralized systems shift the heating and cooling units in or near the occupied space and allow local zone control.
It can be as simple as dedicated split unit (mini split) in each apartment or a centralized primary plant that provides the heating and cooling by means of water or refrigerant to terminal units in the apartment.
Decentralized systems can be very energy efficient because they move heating and cooling energy in either water or refrigerant which has a very low transportation cost as compared to all air systems which can have high fan energy. Some decentralized systems can move heat energy from one part of the building to another (e.g. water sources heatpumps and energy recovery VRF).
Generally there is no false ceiling in an apartment where HVAC equipment can be located. The equipment can be located in closets or other service areas within the apartment. Services for the terminal units such as ducting, water or refrigerant piping can be brought along the corridor or dropped down risers between the apartments. With risers, the apartment on either side can be serviced.
Decentralized systems require a dedicated outdoor air system (DOAS) to deliver ventilation air to the occupied space. The amount of ventilation air is focused on maintaining acceptable indoor air quality and air balance. The amount for indoor air quality is often tied to the number of beds or bathroom fixtures and is spelled out in local codes.
The air balance takes into consideration offsetting ventilation air, kitchen hoods, bathroom exhaust and possibly laundry if it is within the apartment. These airflows are usually variable so the best solutions adjust ventilation airflow to match the real-time exhaust airflow.
Most ventilating units have some form of energy recovery such as a plate heat exchanger or rotor. Units that can recover sensible heat are often referred to as Heat Recovery Ventilators (HRVs). Units that can recover both sensible heat and humidity (latent) energy are referred to as Energy Recovery Ventilators (ERVs).
The ventilating units can be small enough to serve just one apartment (decentralized) or large enough to service the whole building (centralized). Both approaches have strengths and weaknesses noted below.
- Maintenance in control of building owner
- Far fewer envelope penetrations (pressure testing)
- Generally more efficient (Fans, energy recovery device) DOAS units
- Equipment noise away from tenants – easier to attenuate
- Doesn’t use up apartment space
- Cost advantage – project specific
- Operating cost and maintenance is in tenants control
- No common area duct runs
- Minimal fire damper issues
- No common mechanical room requirement – space savings
- Cost advantage – project specific
Leveraging the ventilation system to provide some free cooling is possible for the spring and fall seasons. With some design modifications around 5 Btu/h-ft² can be achieved which can be used to improved he building EUI.
Multifamily and Fancoils
Fan coils are can be used in multifamily buildings. Fan coils can be horizontal type in the bulkhead or entrance or stacked type. Fan coils will require condensate piping. A service access panel will be required for a fan coil in the bulkhead. Stacked units can be serviced through the return air grille.
The ventilation air can be introduced into the return of the fan coil or delivered directly to the space through a supply air grille. Exhaust is typically taken from the bathroom.
Fan coils will require a central heating and cooling plant so the cost to operate the plants must be allocated out through rent or condo fees. The advantage is most of the HVAC equipment is located outside the apartment where it can be serviced without disturbing the occupants or requiring their permission for access.
Multifamily and Water Source Heatpumps (WSHP)
Water Source Heatpumps can be used in multifamily buildings. Heatpumps can be horizontal in the bulkhead or stacked type. Heatpumps will require condensate piping. A service access panel will be required for the heatpump in bulkhead. Stacked units can be serviced through the return air grille. Stacked units typically have a refrigeration cassette in the wall cabinet that can be quickly changed out with a spare to and allow service away from the occupant/homeowner.
The ventilation air can be introduced into the return of the heatpump or delivered directly to the space through a supply air grille. Exhaust is typically taken from the bathroom.
Watersource heatpumps have a small central system whose cost must be allocated to the occupants through rent or condo fees. The bulk of the operating cost will be electricity consumed at the residence. Local energy metering can be desirable for some tenants who wants more direct control of their monthly costs. As well as the maintenance and repair of the heatpumps can be assigned to the tenant. This is often desirable with Condos an other occupant/owner buildings.
Variable Refrigerant Flow (VRF)
VRF can be used in Multifamily buildings. Terminal units can be horizontal type in the bulkhead above the bathroom or entrance. Their wall-mounted terminal units in finished cabinets that can be applied directly to the space. A service access panel will be required for a terminal unit in bulkhead. Condensate piping will be required for the terminal units. Condensate pumps are available for wall-mounted terminal units.
The ventilation air can be introduced into the return of the terminal unit or delivered directly to the space through a supply air grille. Exhaust is typically taken from the bathroom.
VRF systems have centralized outdoor units linked to multiple residences. The operating cost must be allocated to the occupants through rent or condo fees. Several manufacturers can estimate the energy usage in each residence so the cost can be allocated more directly.
Meticulously engineered products to create the best indoor climate
Swegon GOLD Unit with Energy Recovery
The Swegon GOLD ventilation unit is an excellent choice for multifamily residential buildings. It can come with a rotor (RX) or plate (PX) energy recovery or as direct (SD) system. The GOLD unit includes factory-installed and tested unit controls which can be integrated into the hotel building management system via BACnet and several other common protocols.
The GOLD unit is compact and can be installed indoors or out on the roof. It is a leader in energy efficiency with high-performance plenum fans and direct drive EC motors, high-efficiency energy recovery devices and advanced controls algorithms to get the most out of the capital investment.
Swegon GOLD can deliver ventilation air to the residences for fan coils, water source heatpumps, VRF. It can support constant volume or variable airflow for demand control ventilation. Integrating free cooling can be achieved in several ways to help provide free cooling during spring and fall.
GOLD units are Passive House certified for the most demanding performance applications.
Swegon React Dampers
Swegon React Dampers can be used for airflow control to maintain balanced building pressurization and demand control ventilation. React dampers have independent airflow control (airflow remains at require amount regardless on upstream duct pressure). They include a stand alone controller with programming display or can be integrated into the building management system via Modbus.