How to Specify Valve Kits for Fan-Coil and AHU Terminal Units

Sample article. This is placeholder copy outlining the structure of the piece — replace it with content authored or reviewed by the Koolvent engineering team.

Walk through any modern commercial building plantroom and you will find dozens — sometimes hundreds — of fan-coil units (FCUs) and air handling unit (AHU) coils, each requiring a coordinated package of valves and accessories to isolate, balance, control and commission properly. Getting the valve kit specification right at tender stage saves significant time and cost during installation and commissioning.

What a Valve Kit Contains

A standard fan-coil valve kit for a two-pipe or four-pipe coil typically includes:

• Isolation valves — one on the flow and one on the return, allowing the coil to be removed without draining the circuit.
• Commissioning/regulating valve — a calibrated balancing valve (or pressure-independent control valve, PICV) that limits maximum flow to the coil design value.
• Control valve and actuator — modulating (two-port) or diverting (three-port) valve driven by the building management system or local thermostat.
• Strainer — a Y-strainer or in-line filter on the flow connection to protect the coil and control valve from debris.
• Air vent — automatic or manual, at the coil high point.
• Drain point — a drain cock or hose union on the return.

Pre-assembled kits reduce site labour, ensure correct component selection, and allow factory pressure testing before delivery.

Two-Port vs Three-Port Control Valves

The choice between two-port (shut-off) and three-port (diverting) control valves depends on the distribution system design:

Parameter	Two-port	Three-port
System type	Variable flow (VFD pumps)	Constant flow (fixed speed)
Energy use	Lower — pump follows load	Higher — pump runs at full speed
Balancing	Requires PICV or commissioning valve	Simpler — bypasses excess flow
First cost	Slightly higher (PICV)	Lower valve cost

Most modern systems use two-port valves with PICVs, because variable-flow distribution significantly reduces pump energy — often the largest single energy saving available on an HVAC retrofit.

Pressure-Independent Control Valves (PICVs)

A PICV combines the functions of a control valve, commissioning valve and differential pressure regulator in a single body. It:

1. Maintains a constant differential pressure across itself regardless of system pressure variation.
2. Limits maximum flow to the factory-set or site-adjusted design value.
3. Provides linear control authority across its full stroke.

The benefit is that coils cannot over-flow even when neighbouring terminal units close, which eliminates the “robbing” problem common in poorly balanced constant-flow systems. For specifiers, PICVs simplify the specification and remove the need for a separate commissioning set point record — the design flow is locked in at the factory.

Sizing the Control Valve

Control valve sizing starts with the coil design flow rate (litres per second or m³/h) and the available differential pressure. The valve authority (the ratio of valve-fully-open pressure drop to total circuit pressure drop) should be ≥ 0.5 for acceptable control at part load. Low authority causes the valve to behave as though it has only two positions — open and shut — resulting in hunting and poor temperature control.

For a PICV, sizing is simpler: select the valve whose adjustable flow range covers the design flow with margin, and set it at commissioning.

Material and Connection Decisions

• Body material — brass is standard for HVAC duty up to PN16/120 °C; stainless steel for higher temperatures or aggressive fluids.
• Actuator type — spring-return (fail-closed or fail-open for safety on heating coils in frost risk areas); non-spring-return where fail position is not critical.
• Connections — compression fittings for small FCU connections (½” to 1”); flanged or union ends for AHU coils DN25 and above.
• Signal — on/off (2-wire), floating point (3-wire) or modulating 0–10 V or 4–20 mA, depending on BMS specification.

What to Include in a Schedule

A well-prepared valve kit schedule for a tender package includes:

1. Tag number and terminal unit reference.
2. Coil type (heating/cooling/dual) and connection size.
3. Design flow rate and coil pressure drop.
4. Available differential pressure at the index coil.
5. Control valve type (two-port PICV, two-port standard, three-port).
6. Actuator signal and fail-safe position.
7. Isolation valve type and rating.
8. Any special requirements (fire-rated, low-leakage, anti-legionella drain).

Providing this schedule to the valve kit manufacturer allows factory assembly and pressure testing before delivery to site, which reduces installation time substantially.

---

Need valve kits for a fan-coil or AHU project? Request a quote and our team will put together a complete kit schedule and submittal package.