Clarinet

A manifold is a hydraulic manifold that distributes (or groups) hot/cold water flow to several circuits within the same HVAC system: underfloor heating/cooling, radiator loops, fan coil units, air handling unit (AHU) coils, recirculating domestic hot water (DHW) risers, etc. It facilitates balanced distribution, maintenance (isolation valves per outlet), instrumentation (flow meters, thermometers), and compactness in the technical room. When well-designed and insulated, the manifold is a clear and easy-to-understand hydraulic node that saves time… and energy.

Clarinet: definition, components and useful placements

A clarinet consists of a supply collector and a return collector, with multiple connections:

- Basic components : isolation valves on each supply/return, air purge, drain, pressure taps.

- Balancing & measurement : integrated flow meters or downstream balancing/PICV valves, supply/return thermometers, sometimes heat meter per loop.

- Safety & comfort : valve if closed volume, air/mud separator nearby, anti-vibration.

- Finishing : continuous thermal insulation (including elbows/valves), clear loop labeling, color marking (hot/cold).

- Typical installations : underfloor heating cabinet, floor manifolds for radiators, zone manifolds in tertiary buildings, DHW/recirculation manifolds at the base of the column, central manifolds (AHU batteries).

Strengths, limitations and points to consider in a well-designed clarinet

Strengths

• Readability & maintenance: one loop = one valve → quick intervention without shutting down the entire floor.
• Easier balancing: flow rates adjusted as close as possible to the circuits, ΔT maintained.
• Centralized instrumentation: measurement (T°, ΔP, kWh) for control and diagnosis.
• Compactness: shortened networks, controlled pressure losses, clean finishes.

Boundaries

• Local pressure losses if diameter/tap connections are incorrectly sized.
• Cost higher than minimalist "in-line" connections.
• Risk of noise/erosion if speeds are too high at the collector.

Points to consider

• Sizing: choose the body diameter (moderate speed) + center distance of the connections for accessibility; Kvs of the valves adapted.
• Hydraulics: install balancing valves/flow meters, provide pressure taps to adjust at the critical point.
• Water quality: prior descaling, upstream/downstream air/sludge separator, screen filters.
• Expansion & noise: flexible support, speeds < 0.6–1.0 m/s depending on diameter to limit whistling.
• Thermal insulation: continuous including elbows/valves and removable jackets on components; avoid thermal bridges at supports (insulating inserts).
• Accessibility: hatches/cabinets with clearance, lighting, permanent circuit marking; avoid "hidden clarinets".
• Coordination: plan for special connections (drain, purge, bypass), BMS sensors and possible meters per batch (multi-tenant commercial buildings).

Anecdote — "The clarinet that united Aix-en-Provence"

In Aix-en-Provence, an office floor suffered from alternating zones that were too hot and too cold. The radiator supply lines were simply tapped in haphazardly, without any markings. The renovation included the installation of two zone manifolds (supply/return) with flow meters on each loop, pressure taps, isolation valves, and complete thermal insulation. In just one morning of fine-tuning, the flow rates were balanced, the temperature difference (ΔT) was maintained, and subsequent maintenance is now carried out loop by loop without shutting down the entire floor. The building manager said, "We finally have a clear system—and every circuit is working properly."