DHW recirculation

Domestic hot water (DHW) recirculation is a system that continuously (or according to a schedule) circulates hot water from the storage tank/heat exchanger to the risers and then back to the boiler.

The goal is to provide almost instant hot water at the taps, controlled temperatures in long risers, and better management of health risks.

A well-designed system relies on a pump, an insulated network, balancing devices, and anti-scalding mixing valves located as close as possible to the users.

Domestic hot water recirculation: principle, components and key settings

An efficient loop includes: DHW outlet from tank/exchanger, risers and loop returns joining the generator, a circulation pump (often variable speed), balancing valves (or loop temperature regulators), and continuous thermal insulation (including elbows, valves, supports).

Key points to focus on :

- Target temperatures : maintaining a consistent minimum return temperature (comfort & microbiological control); thermostatic mixing valves at the tank outlet and in the showers to limit scalding.

- Balancing : each column return receives its flow rate/ΔT ​​to avoid warm/hot columns.

- Pump : VFD controlled by ΔT supply/return or most unfavorable temperature; time law (reduction at night if compatible with use).

- Measurement & monitoring : temperature probes at strategic points, recordings (BMS/remote reading), air purges.

- Water quality : scale control (hardness), anti-sludge cleaning, screen filters, tank anodes.

- Hygiene : dead points avoided, loop connections rather than "dead ends", procedures for occasional temperature increases if necessary.

ECS loop: advantages, limitations and points to consider

Interests

• Immediate comfort: less waiting → water savings and a better user experience.
• Temperatures maintained: homogeneous columns, stable showers and sanitary facilities.
• Operation: simplified diagnostics (temperature per column, BMS alarms), responsiveness to deviations.

Boundaries

• Heat losses on the network (hence the imperative need for thermal insulation).
• Pumping energy (to be reduced via VFD and schedules).
• Risk of overheating in the technical room if insulation and bypass are poorly treated.

Points to consider

• Continuous thermal insulation including singular points (insulating jackets on valves/flanges, insulating inserts on supports).
• Documented balancing: flow/valve position values ​​per loop, ΔT control.
• Anti-scalding mixers for sensitive uses (showers) + flow restrictors where relevant.
• Clean hydraulics: descaling if old network, clean filters, air purging.
• Control: temperature instructions and time slots adapted to occupancy; alarm on low temperature feedback.
• Design: avoid dead spots/dead arms; loop as close as possible to the last draw-off points.
• Maintenance: checking for scale buildup in heat exchangers/tanks, anodes, pump (bearings/EMI), seasonal recalibration.

Anecdote — “Regular showers at last in Clermont-Ferrand”

In Clermont-Ferrand, a student residence was complaining of lukewarm water on the upper floors in the morning, then excessively hot water in the afternoon. The diagnosis revealed an unbalanced recirculation loop, uninsulated return pipes, and a fixed pump. The team installed thermostatic balancing valves on each return pipe, added a variable frequency drive (VFD) controlled by the lowest temperature setting, improved insulation (including valves and elbows), and installed shower mixers. The result: stabilized water temperature on all floors, waiting time cut in half, and a decrease in kWh consumption thanks to optimized pumping. The manager summarized: "Even during peak hours, the water now circulates exactly as it should."