An energy recovery ventilator works by transferring heat — and, in a total heat ERV, moisture — from the exhaust airstream to the incoming outdoor air before the two streams mix, so the building is ventilated with pre-conditioned air instead of raw outdoor air. In practice that means 68–76% of the heat is recovered across ROTER's published range, and on the CHX-15L vertical unit the gap between sensible and total recovery is 75% against 58% — the 17-point difference that decides whether latent load still lands on your chiller.

 

 

 

 

 

Why ventilation became an energy problem at all

 

 

Buildings got tighter to seal weather out, and in doing so they sealed contaminants in. The response was to ventilate more, and that raised a question HVAC had not had to answer before: how do you move a large volume of outdoor air into a conditioned space without paying to condition all of it from scratch?

 

 

 

The answer is to take the energy out of the exhaust air before it is thrown away. An ERV runs two airstreams in parallel — one out, one in — and puts a heat exchanger between them. The exhaust air gives up its heat; the incoming air picks it up; the two mix only after the exchange has happened. The result is that the cooling or heating plant handles a much smaller temperature difference, and in a total heat ERV it handles a smaller moisture difference as well.

 

 

 

It is worth being precise about the terminology, because it is where most buyers first go wrong. Sensible heat is the energy associated with temperature — you feel it. Latent heat is the energy associated with moisture — you do not feel it, but it has to be removed before the air reaches the room condition. A sensible ERV moves the first; a total heat ERV moves both.

 

 

 

 

 

The three stages of an ERV

 

 

Stage 1 — air is drawn in and out simultaneously

 

 

Two fans run in parallel: a supply fan bringing in outdoor air, and an extract fan removing stale indoor air. The two flows are usually balanced within a few percent of each other, so the building neither pressurises nor depressurises. The ERV's job starts here and never stops — the exchange happens continuously, on every breath the building takes.

 

 

 

Stage 2 — heat and moisture cross the core

 

 

This is where the technology differs, and the three core types are worth understanding separately because they make different trade-offs.

 

 

 

How each core type transfers energy

 

Core type Mechanism Sensible Latent Moving parts Power

Plate — sensible Enclosed aluminium fins form separate supply and exhaust channels; heat conducts through the foil Yes No None None

Plate — total heat Heat exchange paper made of specialty fibres; only small-diameter water vapour molecules pass the fibre gaps Yes Yes None None

Rotary (wheel) A rotating heat-storage matrix carries heat — and moisture — from the exhaust side to the fresh-air side Yes Yes (total-heat rotor) Motor and drive Yes

Heat pipe Sealed copper tubes; a volatile working fluid evaporates at the hot end and condenses at the cold end, moved by gravity Yes No None None

 

 

Two things follow from that table. First, no core mixes the two airstreams — a plate separates them with metal or paper, a rotary transfers energy through the matrix, a heat pipe through a sealed tube. Cross-contamination is a question of core selection, not of quality. Second, the heat pipe is the only core that consumes no power at all, because the working fluid circulates by gravity and phase change rather than by a pump or fan.

 

 

 

Stage 3 — the conditioned airstream is delivered

 

 

By the time the supply air reaches the space, it has already been brought close to indoor conditions. In summer the outdoor air arrives pre-cooled and partly dehumidified; in winter it arrives pre-heated and partly humidified. The ventilation load and the conditioning load both fall.

 

 

 

 

 

What the efficiency numbers actually mean

 

 

Published efficiency figures are quoted at a specific test condition, and knowing that condition is what makes the number usable rather than decorative. ROTER states all figures at GB/T 21087 operating conditions.

 

 

 

GB/T 21087 test conditions used for all published ROTER efficiency figures

 

Season Outdoor dry bulb Outdoor RH Indoor dry bulb Indoor RH

Summer 33°C 80% 26°C 50%

Winter 0°C 30% 20°C 60%

 

 

ROTER's own note on the published tables is worth reading in full, because it is the honest version: "If the operating conditions change, the actual efficiency may fall outside the stated enthalpy recovery efficiency range." So ask for the efficiency computed at your own design conditions. Equivalent calculations at EN 308, EN 16798-3 and ASHRAE 220 conditions can be provided with the relevant test report for a Western submittal.

 

 

 

 

 

Sensible versus total efficiency — the number that decides the spec

 

 

Most published ERV tables give one efficiency figure. That is a problem, because it hides the decision. ROTER's vertical series publishes both, for every model.

 

 

 

ROTER CHX-L vertical series — sensible and total efficiency published separately

 

Model Airflow (m³/h) Static pressure (Pa) Motor power (kW) Sensible efficiency (%) Total efficiency (%) Weight (kg)

CHX-15L 1500 158 0.25*2 75 58 133

CHX-20L 2000 175 0.32*2 76 58 150

CHX-30L 3000 210 0.45*2 75 62 175

CHX-60L 6000 300 1.5*2 76 62 350

CHX-100L 10000 340 3*2 76 70 650

CHX-150L 15000 460 5.5*2 76 70 780

 

 

Read that table carefully and the decision becomes concrete. The CHX-15L is 75% efficient on sensible heat and 58% on total heat — a 17-point gap. In a dry climate with a heating-dominated load, the sensible figure is the one that matters, and a sensible core would be the cheaper choice. In a humid climate with a cooling load, the total figure is the one that matters, and that 17 points is the measurable cost of not recovering moisture.

 

 

 

For comparison, the ceiling-mounted CXH series publishes 68–72% total heat recovery across 1,000–15,000 m³/h.

 

 

 

ROTER CXH series — medium ceiling-mounted total heat recovery unit

 

Model Airflow (m³/h) Static pressure (Pa) Motor power (kW) Efficiency (%) Noise dB(A) Weight (kg)

CXH-10DA 1000 120 0.22*2 72 61 140

CXH-50DA 5000 270 1.37*2 70 63 350

CXH-100DA 10000 400 3.5*2 71 72 670

CXH-150DA 15000 400 5.5*2 70 75 780

 

 

Fresh airflow = exhaust airflow = rated airflow. For reference only. Full 14-model range published on the medium ceiling-mounted page and collected on the specification tables page.

 

 

 

 

 

What the recovery is actually worth in running costs

 

 

The mechanism is clear, but the commercial question is what it is worth. This is where published measurement beats theory.

 

 

 

Measured energy saving — total heat recovery, 200 m² room, Beijing

 

Parameter Value

Outdoor temperature, summer 33°C

Supply air temperature with total heat recovery about 28°C

Supply air temperature with plain ventilation about 7°C

Energy saved, winter approximately 1,112 kWh

Energy saved, summer about 1,427 kWh

Comprehensive annual saving approximately 42.3%

Electricity price used ¥0.48/kWh

 

 

The important detail is the supply air temperature. Without recovery, the supply air arrives at about 7°C and the cooling plant has to remove all of that load. With recovery it arrives at about 28°C, so the same space is conditioned from a far smaller starting delta. That is where the 42.3% comes from — not from a cleverer fan.

 

 

 

 

 

What an ERV does not do

 

 

It is worth being clear about the limits, because a common misunderstanding costs money later.

 

 

 

It does not reduce the ventilation requirement. An ERV recovers energy; it does not ventilate less. The fresh air volume is whatever the building needs for air quality.

 

It does not filter the air. Filtration is a separate section, and it is a specification decision of its own.

 

It does not eliminate the cooling or heating load. It reduces it. In a 35°C outdoor design condition, pre-cooling the air to 28°C leaves a 7°C delta to close, not zero.

 

It does not work below the dew point without a desiccant core. Refrigeration dehumidification is limited to roughly a 0°C dew point because the coil must stay above freezing. Below that, a rotary desiccant wheel is the technology, reaching −70°C.

 

 

 

 

 

Choosing the core: a short decision path

 

 

Does the building have a meaningful cooling load? If yes, and the climate is warm or humid, a total heat core is the right answer — see the ERV vs HRV comparison for the full decision path.

 

Is the exhaust clean and the cross-contamination risk low? If yes, a plate core. It has no moving parts, nothing to wear out, and nothing to maintain beyond filters.

 

Is the airflow large or the duct pressure high? If yes, a rotary core handles it more economically as a single unit, and the ECW version tolerates exhausts up to 300°C.

 

Is the exhaust dirty, dusty or corrosive? If yes, a heat pipe core — low air resistance, effective condensate drainage, and no moving parts to foul.

 

Does the process need a low dew point? If yes, add a rotary desiccant dehumidifier to the ventilation. See the industrial rotary dehumidifier guide.

 

 

 

 

 

Core components of an ERV

 

 

The heat exchanger is the heart of the unit, but it is not the whole of it.

 

 

 

What else is in the cabinet

 

Component What it does What to specify

Supply and extract fans Move the two airstreams in parallel Forward-curved centrifugal for low noise at high airflow; EC or VFD where part-load modulation matters

Filters Clean the supply air and protect the core Grade by the process — primary, medium, high-efficiency, sub-HEPA

Heat exchange core Where the energy transfer happens Plate, rotary or heat pipe; sensible or total heat

Motors Drive the fans AC, EC or VFD — EC allows stepless modulation

Controls and sensors Coordinate the fans and the outside air Differential pressure sensing, CO₂ demand control, BMS/BACnet integration

Coil and drain (in AHU formats) Condition the airstream further U-shaped drain trap before external piping; sliding bases so the coil can be withdrawn for service

 

 

 

 

Case studies: what this looks like in practice

 

 

Theory is easy; the projects are what prove it. ROTER's project record includes the largest single supply of ventilation units in its history.

 

 

 

ROTER project references with published quantities

 

Project Scale Application

Wuhan Huoshenshan Hospital 880 ventilation units Hospital, emergency build

Hangzhou Asian Games 74 air-cooled heat-pipe heat recovery units Sports venue, fifth major international event

Beijing Olympic Games (2008) First international sporting-event HVAC project Sports venue

Nanjing Youth Olympic Games (2014) Second Sports venue

Wuhan Military World Games (2019) Third Sports venue

Beijing Winter Olympic Games (2022) Fourth Sports venue

Heze Fangcang Shelter Hospital Field hospital Healthcare

National Cybersecurity Talent and Innovation Base Phase II High-performance building Data-centre adjacent

 

 

Two of these are worth drawing out. The 880 units for Huoshenshan Hospital were delivered during the emergency build — a reference that demonstrates delivery at scale, to a schedule measured in weeks, into a live medical facility. The 74 heat-pipe units for the Hangzhou Asian Games were ROTER's fifth participation in a major international sporting-event HVAC project, and a heat pipe core is specifically the choice where a large volume of fresh air has to be conditioned across a wide, high space without extensive ductwork.

 

 

 

 

 

Frequently asked questions

 

 

What is an energy recovery ventilator?

 

An energy recovery ventilator, or ERV, is a system that employs energy recovery technology, such as a static-plate core or rotating wheel. The process uses balanced airflows and recovers otherwise-expended total energy comprised of heat (sensible energy) and humidity (latent energy). In summer, warm and humid outside air is pre-cooled and dehumidified via the total energy from the outgoing cool interior air. In winter, cold and dry outside air is preheated and humidified via the total energy from the outgoing warm interior air. Subsequently, less energy is needed for conditioning and ventilation, which means HVAC equipment can be downsized.

 

 

 

How does an ERV work?

 

Two fans run in parallel — one supplying outdoor air, one extracting stale indoor air. A heat exchanger sits between the two airstreams. The exhaust air gives up its heat to the core; the incoming air picks it up; the streams mix only after the exchange. In a total heat ERV, moisture is transferred as well, so the incoming air is pre-cooled and dehumidified in summer and pre-heated and humidified in winter. The conditioning load on the chiller and boiler therefore falls, which is what allows the plant to be downsized.

 

 

 

What is the difference between an ERV and an HRV?

 

An ERV recovers both sensible heat (temperature) and latent heat (moisture) from exhaust air. An HRV recovers sensible heat only. In practice an ERV is used for commercial buildings with air-conditioning loads, and an HRV for residential buildings in cooler climates where heating is the dominant load and dehumidification is not required.

 

 

 

What efficiency should I expect?

 

Across ROTER's published range, total heat recovery efficiency is 68–76% measured at GB/T 21087 operating conditions. Sensible heat efficiency is higher — the vertical CHX-L series publishes 73–76% sensible against 58–70% total for the same units. Because efficiency depends on the conditions, ask for the figure calculated at your own design outdoor and indoor conditions rather than accepting the catalogue value.

 

 

 

How much energy does an ERV actually save?

 

In a documented 200 m² room in Beijing, supply air arrived at about 28°C when the outdoor temperature was 33°C, compared with about 7°C for plain ventilation which would have required further cooling. Approximately 1,112 kWh was saved in winter and about 1,427 kWh in summer — roughly 42.3% comprehensive annual saving at ¥0.48/kWh.

 

 

 

Can an ERV be used in a hospital or data centre?

 

Yes, and it is often the reason one is specified. For hospitals and data centres the requirement is normally a combination of temperature control, low humidity and strict cross-contamination control, which points to a plate total heat exchanger combined with dedicated dehumidification where the dew point must be held low. For data centres, the combined rotary AHU and commercial air conditioning unit series are the relevant ranges. See the hospital heat recovery ventilation page for the full application detail.

 

 

 

What maintenance does an ERV need?

 

It depends on the core. A plate heat exchanger has no moving parts, so maintenance is limited to filter replacement and periodic inspection of the core for fouling; dust and foreign matter on the elements can be removed with a vacuum cleaner. A rotary unit additionally needs periodic rotor inspection and cleaning. A heat pipe exchanger is maintenance-free apart from filters.

 

 

 

Do you supply the efficiency at EN 308, EN 16798-3 or ASHRAE 220 conditions?

 

Yes. The published figures are stated at GB/T 21087 conditions, and equivalent calculations at EN 308, EN 16798-3 or ASHRAE 220 conditions can be provided together with the relevant test report, so the unit can be specified into a Western submittal package. ROTER holds ISO 9001, ISO 14001 and ISO 45001 management system certification and CE certification for rotary wheel heat recovery units.