American Edge Engineers ·
The short answer
For a single-storey restaurant or shop with its own roof, packaged rooftop units are usually the simpler choice. One unit cools, heats and brings in outdoor air for a zone, and most landlords and franchise prototypes are already set up for them.
VRF earns its place when a space has many small rooms that each need their own control, when there is little or no roof to use, or when the owner wants all-electric heat pumps. Many buildings use both: VRF for room-by-room comfort, and rooftop or dedicated outdoor-air units for ventilation.
How each system works
Packaged rooftop units
A rooftop unit (RTU) is a single packaged box on a roof curb. It holds the compressor, coils, fan and filters, takes in outdoor air, and sends conditioned air through ducts to the space below. Heating can be gas, electric or a heat pump. One unit normally serves one zone with one thermostat, so a large space is split into zones by using several units.
VRF heat pumps
A variable refrigerant flow (VRF) system connects one outdoor heat pump to many indoor units through refrigerant piping. Each indoor unit has its own control, and the outdoor unit varies its output to match what the rooms are asking for. Heat recovery versions can heat some rooms while cooling others.
VRF indoor units recirculate room air. They do not bring in outdoor air by themselves, so a VRF building still needs a separate ventilation system.
Side by side
| Rooftop units | VRF heat pumps | |
|---|---|---|
| Zones | One zone per unit | One zone per indoor unit, often dozens on one system |
| Outdoor air | Built in, usually with an economizer for free cooling | Needs a separate outdoor-air unit or ventilator |
| Heating | Gas, electric or heat pump | Heat pump (all-electric) |
| Roof | A curb and a structural check for each unit | Fewer, smaller outdoor units; they can also sit on the ground or a setback |
| Distribution | Supply and return ducts from the roof | Small refrigerant pipes to each room, plus smaller ducts |
| Kitchen make-up air | Can be provided by a rooftop or make-up air unit | Not suited; a separate make-up air unit is needed |
| Maintenance | Standard equipment that most service contractors know | Needs technicians trained on that VRF system |
| Best fit | Open sales floors, dining rooms, single-tenant boxes | Clinics, offices and other spaces with many small rooms |
Restaurants: the kitchen decides a lot
A commercial kitchen hood exhausts a large amount of air, and every cubic foot has to be replaced with make-up air. That air comes from outdoors, often needs tempering in cold weather, and is delivered by a dedicated make-up air unit or a rooftop unit. VRF indoor units are not designed to handle it.
The dining room has the same pattern on a smaller scale: it is full of people, so ventilation and cooling loads follow the occupancy. A rooftop unit with an economizer handles that well, which is why most quick-service prototypes use them. VRF can still make sense for the offices, break rooms and storage at the back. Our quick-service restaurant MEP checklist covers the hood, make-up air and the rest of the kitchen.
Retail, clinics and offices
A shop with one open sales floor is a single zone and suits a rooftop unit. A medical or dental clinic, or an office suite, is different: exam rooms, offices and treatment rooms each have their own loads and want their own thermostat. That is where VRF works well, with a separate unit bringing in the outdoor air.
VRF also helps when the tenant space is inside a multi-storey building. The outdoor unit can go on the roof, a setback or the ground, and the refrigerant piping is much smaller than ductwork. The piping length and the height between units have limits set by the manufacturer, so check them early: in a house in Mill Basin, Brooklyn, the longest refrigerant run was 38 ft against a 394 ft limit.
What to check before choosing
These are the questions that usually settle the choice:
- The landlord's rules for rooftop equipment, curbs, roof loads and penetrations
- Whether existing rooftop units can be reused or replaced like for like
- Room-by-room loads, so the number of zones is known before the system is chosen
- Where the outdoor air comes from, and the kitchen make-up air if there is a hood
- The electrical service, especially when gas heating is replaced by heat pumps
- Refrigerant limits for small rooms served by VRF, under the mechanical code in force
- Energy code requirements, such as economizers on larger rooftop units
- Local rules on gas equipment in new buildings, which some cities now limit
- Who will maintain the system, and whether that service is available nearby
What our projects show
In practice the answer is often both. At the Forest Hills ambulatory facility in Queens, a VRF system of six outdoor units, about 104 tons, serves more than 70 indoor units, so every exam room, recovery bay and office has its own control. Seven gas-fired rooftop units (six 7-ton and one 16-ton) with hot-gas reheat and economizers carry the outdoor air for the clinical floors, and three energy-recovery ventilators serve the rest of the building.
The public safety center in Northern California goes the other way: 15 packaged rooftop heat pumps, one or two for each major area including the kitchen and dining room, each with an economizer and an outdoor-airflow monitoring station. Three dedicated units supply 100% outdoor air, and two VRF condensing units serve about twenty fan coils in the offices and the fire-crew dorms, where each room needs its own control.
In a warehouse with offices in the Bronx, the brief was fresh air without a large rooftop unit. Two 10-ton VRF heat pumps, one per floor, serve eight ducted indoor units, and a 540 cfm outdoor-air fan with an electric duct heater on each floor brings in the ventilation air.
Common questions
Can a VRF system bring in fresh air?
Not by itself. VRF indoor units recirculate room air, so outdoor air comes from a dedicated outdoor-air unit, an energy-recovery ventilator or a rooftop unit, sized to the ventilation the code requires for each space.
Is VRF more efficient than rooftop units?
VRF often runs efficiently at part load, and heat recovery can move heat between rooms. The real difference depends on the building, the climate and the equipment chosen, so compare the options in an energy model or compliance check rather than from general claims.
Can a gas rooftop unit be replaced with a heat pump?
Usually, yes. Packaged rooftop heat pumps fit on similar curbs, but check the heating capacity at your winter design temperature and whether the electrical service can carry the extra load.
How do I know how many zones or tons I need?
From a room-by-room load calculation. It sets the size of each unit and shows which rooms behave differently enough to need their own zone. If that is all you need, order an HVAC load calculation on its own.
Get the choice checked
Send one drawing set with the landlord's criteria and we will tell you which system fits, what the roof and electrical service need, and what the drawings must show, as part of a free franchise MEP review.
Next step
Learn how our MEP Design for Franchise Projects service works, or send us one drawing set for a free project review and decide after you see our work.