Heat recovery VRF vs heat pump VRF

Variable refrigerant flow systems come in two main configurations. In a heat pump VRF system, all indoor units connected to one outdoor unit operate in the same mode: they all heat or they all cool. In a heat recovery VRF system, individual indoor units can heat or cool independently, and the system moves heat from zones that need cooling to zones that need heating.

The choice affects first cost, comfort, energy use and how the building must be zoned. Neither type is better in every case. The right answer depends on how often the building has heating and cooling demands at the same time, and on whether zones with different needs can be grouped onto separate systems.

How heat pump VRF works

A heat pump VRF system uses two refrigerant pipes, a liquid line and a gas line, running from the outdoor unit to the indoor units. The outdoor unit sets the system mode based on a priority rule, for example majority demand, a master thermostat or outdoor temperature.

When the system is in cooling mode, indoor units calling for heat cannot get it. They typically switch their fans to low or off and wait until the system changes over. That is acceptable when all zones on the system have similar loads, such as:

• Rooms facing the same orientation
• Interior zones with similar internal gains
• Spaces with similar occupancy schedules

It becomes a comfort problem when one system serves zones with very different loads, for example a south-facing perimeter office and a north-facing one on a sunny day in spring, or a meeting room full of people next to an empty office.

How heat recovery VRF works

Heat recovery VRF adds the ability to serve heating and cooling simultaneously. Manufacturers use two main approaches:

• Three-pipe systems use a liquid line, a high-pressure hot gas line and a low-pressure suction gas line. Branch selector boxes at each zone or group of zones connect the indoor unit to the appropriate lines for heating or cooling.
• Two-pipe systems use a central branch controller that separates refrigerant into liquid and gas and distributes it to indoor units in either mode.

When some zones cool and others heat, the heat absorbed by the cooling units is rejected into the refrigerant that feeds the heating units. The outdoor unit only has to make up the difference between total heating and total cooling. In a perfectly balanced condition, the compressor mainly moves heat around the building, with the outdoor coil doing little work.

Comparing the two

When heat recovery pays off

Heat recovery VRF earns its extra cost when there are many hours with simultaneous heating and cooling. Typical situations include:

• Shoulder seasons in Canadian climates, when sunny perimeter zones need cooling while shaded or north zones need heating
• Buildings with large interior zones, such as deep floor plates where core areas need cooling all winter while the perimeter needs heat
• Hotels and multi-unit residential buildings, where guests or residents set very different temperatures
• Buildings with server rooms, kitchens or equipment rooms on the same system as general space
• Mixed-use floors with meeting rooms, offices and amenity spaces

The benefit is smaller in buildings with uniform loads, small floor plates with mostly perimeter zones of the same orientation, or climates and seasons where the whole building needs the same mode. An hourly energy model is the best way to estimate how much heat can actually be recovered.

Zoning decisions

Zoning is where the two system types differ most in practice. Our guide to zoning a commercial building covers the general principles; for VRF the key points are below.

Zoning for heat pump VRF

To make a heat pump VRF system comfortable, each outdoor unit should serve zones that are likely to want the same mode at the same time.

1. Group zones by orientation: separate systems for north, south, east and west perimeters where loads differ significantly.
2. Keep interior zones, which need cooling most of the year, on their own systems.
3. Put rooms with unusual loads, such as server rooms or conference rooms, on separate systems or provide them with dedicated cooling.
4. Choose a sensible changeover method and deadband to avoid frequent mode switching, which reduces efficiency and causes comfort complaints.

This often means more outdoor units, which partly offsets the first-cost advantage of heat pump VRF.

Zoning for heat recovery VRF

Heat recovery systems can mix zones freely, but there are still practical limits:

• Each branch selector port typically serves one zone or a group of indoor units that must share a mode. Grouping too many units on one port recreates the heat pump problem at a smaller scale.
• Large mixed systems carry large refrigerant charges, which must be checked against CSA B52 concentration limits in the smallest room served. See our guide to VRF piping and CSA B52.
• Branch selector boxes must be accessible for service and can produce some noise during mode changes, so locate them away from quiet rooms.

Cold climate considerations

In the coldest weather, both system types rely heavily on the outdoor unit to extract heat from outdoor air, and simultaneous cooling demand is usually small. The heat recovery advantage is largest in shoulder seasons and in buildings with constant internal cooling loads. In Prairie and northern locations, both types typically need supplementary heat or a cold climate outdoor unit for design conditions.

Water-source VRF, which connects the outdoor units to a building water loop, extends the heat recovery concept: heat can be exchanged between separate VRF systems through the loop, and a boiler, heat pump or ground loop can supply the remaining heat.

Ventilation interaction

Both types usually need a separate ventilation system. If a dedicated outdoor air system delivers air at a neutral temperature, it reduces the risk that ventilation air pushes zones into opposite modes. Delivering cold ventilation air in winter to zones served by a heat pump VRF system can create unexpected mode conflicts.

Frequently asked questions

Can a heat pump VRF system be converted to heat recovery later?

Generally not without replacing outdoor units and adding branch controllers and possibly a third pipe. It is much easier to make the decision at design stage.

Is heat recovery VRF always more efficient?

Not always. It can recover heat when loads overlap, but it has extra components and pressure losses. In buildings with little simultaneous demand, a well-zoned heat pump system may perform similarly at lower cost.

Which is better for a hotel?

Heat recovery VRF is common in hotels because guest preferences vary widely. Heat pump VRF can work if systems are carefully grouped, but complaints during shoulder seasons are more likely.

Key takeaways

• Heat pump VRF serves all zones on a system in one mode; heat recovery VRF can heat and cool different zones at the same time.
• Heat recovery costs more but can save energy and improve comfort when simultaneous heating and cooling is frequent.
• Heat pump VRF requires careful zoning by orientation and load to avoid comfort complaints.
• Refrigerant charge limits under CSA B52 still apply to both types and influence how systems are divided.
• Use an hourly energy model to estimate heat recovery potential before choosing.