{"id":9161,"date":"2026-07-27T18:54:06","date_gmt":"2026-07-27T15:54:06","guid":{"rendered":"https:\/\/alphatech.com.gr\/?p=9161"},"modified":"2026-07-30T10:10:08","modified_gmt":"2026-07-30T07:10:08","slug":"diodi-i-triodi-vana-sta-fan-coil-i-apantisi-kryvetai-sto-buffer-sas","status":"publish","type":"post","link":"https:\/\/alphatech.com.gr\/en\/diodi-i-triodi-vana-sta-fan-coil-i-apantisi-kryvetai-sto-buffer-sas\/","title":{"rendered":"Two-way or Three-way Valves in Fan Coils? The Answer Lies in Your Buffer"},"content":{"rendered":"
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Whether to use a two-way or three-way valve on a fan coil unit is not a matter of preference, but of hydraulic design. Find out how each one works, what you gain from IVAR VFC valves (two-way and three-way) and a simple selection rule that depends on one thing: whether the system has a buffer tank or not.<\/strong><\/span><\/em><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Why does every fan coil unit need a valve?;<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The fan coil unit provides heating or cooling only when the room requires it. The thermostat must be able to cut off the water supply to the unit once the desired temperature has been reached. Without a valve, water circulates continuously through the unit; the fan coil unit continues to operate via natural convection even when we do not want it to, and temperature control becomes inaccurate.<\/p>

In a system with multiple fan coils, it is also the valve that allows for independent control in each room. The question, therefore, is not if<\/em> We\u2019ll fit a tap, but what sort of<\/em>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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The role of Kv: why correct sizing is crucial for flow<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The Kv (valve flow coefficient) indicates how much water flows through the valve for a given pressure drop. It is very easy to make the following mistake here: an undersized central zone solenoid valve \u00abchokes\u00bb the entire zone, resulting in uneven distribution, noise and underperformance at the most remote outlets.<\/p>

The solution is not a large central valve, but a correctly sized valve with a suitable Kv value on each fan coil unit<\/strong>. The selectable Kv rating of the IVAR VFC valves allows you to match the valve to the flow rate of each unit and achieve true hydraulic balancing, whilst for large fan coils, the high-flow VFC 02 (Kv up to 4.50) handles high flow rates without pressure drop. The valves can also be grouped on a manifold for centralised, accessible control.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Valve diodes (IVAR VFC 01 \/ VFC 02): cut off the flow<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The diode is a two-way axial valve fitted to the return pipe of the fan coil, together with an electrothermal head. When a signal is received from the thermostat, completely cuts off the flow<\/strong><\/span> towards the element. The network operates with variable flow<\/strong>:<\/span> The more fan coils that are switched off, the less water circulates.<\/p>

It is simple, economical and has fewer connections.<\/p>

What you need to bear in mind:<\/strong><\/span> If several diodes are switched off at the same time, the total power supply to the heat pump drops, and this is precisely where the buffer comes into play, as we shall see below.<\/p>

IVAR data: <\/strong><\/span>The VFC 01 (G\u00bd\u201d or G\u00be\u201d) is available with a selectable Kv value ranging from 0.25 to 2.10, whilst the VFC 02, designed for high flow rates (high flow, G\u00be\u201d) offers Kv values of 2.10 \/ 3.20 \/ 4.50. This allows you to select the correct Kv for the flow rate of each fan coil and balance the system.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\"Interior\t\t\t\t

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Three-way valve (IVAR VFC 03): diverts the flow to the bypass<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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A three-way valve is a valve with 4 connections<\/strong> <\/span>which can be fitted either before or after the fan coil. In response to a signal from the thermostat, the electrothermal actuator moves the piston and the valve operates in two modes: feeding<\/strong> <\/span>\u03ae by-pass<\/strong>.<\/span><\/p>

The key point is this: once the room has reached the desired temperature, the water It does NOT pass through the element<\/strong>.<\/span> It is diverted via a bypass except<\/em> from the fan coil and is returned to the system. In this way, we achieve two things at once: the unit is isolated and cooled (correct control), whilst the flow in the primary circuit remains almost constant<\/strong>.<\/span> This steady flow is the main advantage of the triode.<\/p>

IVAR data: <\/strong><\/span>The VFC 03 (G\u00bd\u201d or G\u00be\u201d) is available with a Kv rating ranging from 0.25 to 2.50 and a piston stroke of 3 mm.<\/p>

Both series share the same technical limits: maximum temperature 120 \u00b0C, maximum pressure 10 bar, maximum differential pressure with an electrothermal head fitted of 1.5 bar, and fluids ranging from water to 50%. They are driven by the same on\/off electrothermal head with M30\u00d71.5 thread<\/strong> <\/span>the same model as the underfloor heads, so they can be sourced from the same stock and are easy to replace.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\"\u03c4\u03c1\u03af\u03bf\u03b4\u03b7\t\t\t\t

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Please note: wall-mounted fan coils with a built-in room sensor<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Many wall-mounted fan coils have a temperature sensor built into the machine<\/strong><\/span> (in the path of the intake air). If water continues to flow through the element whilst the fan has stopped, the hot\/cold element affects the air around it, the sensor \u00abreads\u00bb the element instead of the room, and naturally does not function correctly.<\/p>

The point here is clear: once the room has reached the desired temperature, you must the flow of water through the element stops<\/strong>.<\/span> Both valves can achieve this, but in different ways. The two-way valve does so by cutting off the flow, whilst the three-way valve diverts it via a bypass outside the valve body. What you must absolutely avoid is continuous water flow through the element (e.g. without a valve or with incorrect wiring). For this reason, in systems with a built-in sensor, a valve with an electrothermal head is not a luxury but a necessity.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t

The simple rule of thumb: it all comes down to the buffer<\/h2>\n\t\t\t\t
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If you take just one thing away from this article, let it be this:<\/p>