1) Manifold

The temperature of the mixed hot water that circulates around the underfloor heating system can be controlled either at the manifold or at the main boiler. If it is to be controlled at the manifold, a Floor Mixing Manifold will be required which comes complete with a blending valve and a circulating pump.

If the temperature of the mixed hot water is to be controlled from the boiler – usually as part of a BMS system – then a manifold without a blending valve and pump set will be required. This assumes that the boiler has a pump that is sufficiently powerful to circulate the water around the underfloor heating system.

Floor Mixing Units

Best practice for installing underfloor heating is to run continuous loops of pipe for each room or part of the room, with the flow and return from each loop of pipe being brought back to a manifold where it connects into the system.

Underfloor Heating System Manifold

In the illustration above, the various components have been identified. When the room thermostat calls for heat, it has the effect of completing an electrical circuit and sends a signal to the wiring centre. The actuators are connected to the wiring centre, which then sends a signal to the boiler to send hot water. At the same time it sends a signal to the pump to start up. After a short time, the actuator opens up to allow the mixed hot water into the loop that is calling for heat.

Ball Valves

The hot water from the boiler arrives at the manifold and passes through the ball (isolating) valve; these valves are essential for isolating the manifold especially at the time of installation and before the boiler is installed. By keeping the manifold isolated, the underfloor heating system can be pressurised and screeding, if required, can commence.

When the boiler is being connected to the underfloor heating system it is essential to purge the air from the flow and return pipes prior to opening the ball valves. Failure to do so will result in air entry to the underfloor heating system and compromise its performance.

Blending Valve

Water from the boiler arrives at the blending valve at a temperature of 80degC. Water that has been around the loop returns to the blending valve at 35degC. The flow and return water passes through the mixing chamber of the blending valve and enters the loop that is calling for heat.

Blanking Plate

As the mixed water leaves the blending valve, a blanking plate prevents the water from returning to the boiler.

Grundfos Pump

When the room thermostat calls for heat, it sends a signal to the wiring centre, which in turn signals the boiler to send hot water. The wiring centre at the same time signals the pump to circulate the mixed hot water. The relevant actuator(s) open to allow the mixed hot water to circulate around the loops that require heat.

Pressure Gauge

Once the underfloor heating system has been installed the system is pressurised, usually to 3 bar. When the screeding is in progress, frequent checks need to be made on the pressure gauge. In the event that a pipe is punctured, the pressure gauge will automatically return to zero. As each trade works on the floor, the pressure gauge should be frequently checked.

Filling/ Drain Bibcock

Once all of the pipe has been connected to the manifold, the isolating valves and individual loops should be closed before turning on the water supply via a hose pipe connected to the bibcock. Each loop in turn should be opened and the air purged in turn from the system via the air vents.

Adjustable Balancing Valves

Underfloor heating systems are largely self balancing, but there are occasions when systems do need to be manually balanced. Balancing valves determine the flow of water around individual loops and are left fully open.

In the first instance the red cap is removed, turned upside down and replaced. When turned anti-clockwise, the flow rate is increased up to 4 litres per minute. There is an allen key fitting on the top of the balancing valve which can be further adjusted to increase the water flow between 4 – 8 litres per minute.

Actuators

Actuators allow individual circuits to operate independently of each other. This allows one manifold to service a number of zones, so heat can be supplied to some rooms (or zones) that are occupied and require heat while other rooms that are not in use will not require heat.

Actuators are connected to the wiring centre. Item 4 of the Fitting Instructions shows that the red Actuator Indicator will rise between half a millimetre and several millimetres to allow the mixed hot water into the loop that requires heat.

Cut Off & Balancing Lockshield

This determines the amount of water that is allowed back to the boiler and it is left fully open. It balances the secondary circulating pump on the manifold with the primary pump on the boiler. If the primary pump is very powerful and is pushing against the circuit it can be throttled back to correct the water pressure imbalance between the primary and secondary pump.

Return Bypass

If the system does not require any more of the water that is flowing back to the manifold, instead of entering the blending valve, if flows down the return pipe, bypasses the blanking plate and flows back to the boiler.

MANIFOLDS WITHOUT PUMPS & TMV’S

In circumstances where mixed water is being delivered to the manifold and is pumped around the underfloor heating system, there is no requirement to fit a circulating pump or thermostatic mixing valve to the manifold. This is usually the case where a BMS heating system is the heat source or where air or ground source heat pumps are the heat source.

This assumes that the primary pump is sufficiently powerful to circulate water around the underfloor heating system; in circumstances where the primary pump is not sufficiently powerful, it is necessary to put a secondary pump on the manifold.

New Developments for Manifolds

Plastic manifolds are starting to appear in the British Market.  
However, we only supply manifolds made from nickel plated brass for quality resilience and reliability.

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