Understanding heat recovery from a chiller and its value for domestic hot water
Where the "lost" heat comes from: condenser, extract air, cooling water
A chiller produces cooling, but it also rejects heat. It mainly leaves via the condenser, through air blown outdoors or through a cooling water loop. Depending on the installation, heat can also be captured from air extracted from a plant room, or from condensation water when the system is water-cooled. This heat isn't "free," but it is recovery of energy already paid for by the compressor.
What you can heat: domestic hot water preheating, backup and return loop
The simplest route is to preheat domestic hot water upstream of the tank, to reduce the work the backup source (electric, boiler, heat pump) has to do. On some sites, recovery can also feed a low-temperature backup or stabilise the return loop, keeping the water warm without over-consuming.
Expected gains on your jobs: kWh recovered, lower bills and comfort
Gains depend on the chiller's running hours and domestic hot water needs. The target is often several thousand kWh/year on continuous-use sites. The result: a lower bill, better-controlled power peaks, and more consistent hot water, especially in commercial buildings, kitchens, shops or small multi-unit buildings.
Choosing the right recovery solution based on the existing installation
Direct recovery on the condenser: plate exchanger, buffer tank, controls
If the condenser is accessible, the most cost-effective recovery is direct. Fit a plate exchanger on the water side, add a buffer tank to stabilise flow rate and temperature, then controls that keep cooling as the priority. A 3-way valve and condensation limit often make the difference.
Desuperheater and partial recovery: when it's easier to integrate
A desuperheater on the discharge line gives partial recovery, easy to add without modifying the condenser. It's useful for preheating domestic hot water or a loop return when needs are irregular. Don't size your entire heating system around it.
Special cases: water/water chillers, cooling towers and hydraulic networks
For a water/water chiller, recovery is treated as an exchange between two hydraulic loops. With cooling towers, isolate the heat circuit in a closed loop and monitor fouling, corrosion and sanitary risks. On an existing network, validate flow rates, pressure losses and temperatures.
Sizing and points to watch for effective recovery (with no bad surprises)
Assessing domestic hot water needs and usage profiles: flow rates, schedules, temperatures
Start by measuring your actual domestic hot water needs. Look at draw-off flow rates, morning and evening peaks, and the target temperature. Well-sized recovery mainly covers the peaks, without overheating the tank. Aim for a setpoint around 55 to 60°C, with a mixing valve if needed. The right volume depends on usage, not gut feel.
Refrigeration compatibility: superheat, subcooling, pressures and safety
Recovery must not destabilise the refrigeration unit. Check superheat and subcooling after installation. Monitor pressures and condensation temperature, especially in summer. Plan for an exchanger and safety devices suited to the refrigerant, the pressures, and the frost risk. Stability takes priority over the advertised gain.
Water quality and maintenance: scaling, corrosion, treatment and access
Hard water quickly fouls an exchanger and reduces efficiency. Anticipate scaling, corrosion, and access for descaling. Filtration, a softener or targeted treatment can be useful. Also consider the anode, drain valves and measurement points. Simple maintenance avoids callbacks.
Implementation on site: steps, settings and performance monitoring
Schematic diagrams: exchanger position, valves, circulators and check valves
On the diagram, place the exchanger as close as possible to the heat source, with isolation valves on both sides to make maintenance easier. Add a filter, a circulator sized to the useful flow rate, and a non-return valve to avoid parasitic loops. Also plan for drain points and a relief valve if the circuit can build up pressure. The goal: stable recovery, with no hydraulic "short circuit."
Controls and priorities: domestic hot water setpoints, backup management and anti-legionella
Set the domestic hot water setpoint according to usage and storage volume. Enable domestic hot water priority only if it doesn't degrade heating comfort. The electric or boiler backup must remain a fallback, with clear thresholds and time delays. Programme an anti-legionella cycle suited to the generator and the tank, preferably during off-peak hours.
Measurements to record: temperatures, flow rates, energy recovered and proof of results
Record at minimum flow and return temperatures, flow rate (or validated circulator speed), and energy meters where possible. Note the final settings, valve tests, and readings under steady-state conditions. A simple file, with photos, values and dates, serves as site evidence for the client and for grant applications.
Profitability and grants in 2026: how to price and secure your application
Quick profitability calculation: kWh recovered, savings, payback time and risks
Calculate it in 3 lines. Targeted annual kWh (production or recovery) multiplied by your price per kWh. Add a margin for actual usage. That gives you the annual saving. Divide the remaining cost by that saving to estimate the payback time. Keep a "risks" line (maintenance, setting drift, weather, tariff changes) to avoid overly rosy promises.
CEE and other schemes: conditions, supporting documents and common mistakes in 2026
In 2026, secure the application from the quote stage onward. CEE approval before commitment, an RGE-certified company if required, and full traceability. Keep the dated quote, detailed invoice, proof of qualification, technical sheets, photos if useful, and a signed sworn statement. Common mistakes: quote signed too early, missing CEE technical sheet reference, non-compliant equipment, inconsistent dates.
Client pitch: environmental impact, compliance and added value for the installation
With the client, keep it concrete: lower bills, comfort and property value. Highlight compliance (RGE, best practice) and the quality of commissioning. A clean file means an insurable installation that's easier to sell on, like a well-kept maintenance log.
Key figures
30 to 50%
Recoverable waste heat
20 to 40% of hot water
Savings
40 to 60°C
Temperature
Frequently asked questions
In practice, recovery mainly serves preheating: you often target an outlet temperature of 25–45°C depending on the condensation regime and flow rates. To reach the regulatory 55–60°C in storage (and higher for anti-legionella cycles), you generally need a backup source (electric, boiler or heat pump).
Louis Meneteau
CPO of Argile
