Introducing the Thermo-Differential Valve
The Thermo-Differential Valve by Conico Valve Technology is a unique self-actuating 3-way switching valve that presents a very effective, reliable and economic method of enhancing the thermal layering (stratification) in thermal storage systems with variable input temperatures (e.g. solar thermal), or multiple input temperatures (e.g. space heating & domestic hot water combi-systems), thereby boosting their performance and thermal efficiency. The Thermo-Differential Valve is installed directly on the storage tank inlet and uses an extremely reliable switching mechanism to direct the flow to different levels in a storage tank, based on the temperature difference between the water flow through the valve and the water inside the storage tank, as illustrated by the animation below.
- Press PLAY to see the three Thermo-Differential Valves switching position as the conditions change
- Under bright sunlight, the Thermo-Differential Valve directs the solar return-flow into the top inlet of the tank
- As the temperature of the solar return-flow drops and falls below the storage tank temperature at the top inlet, the return-flow is bypassed to a lower inlet into the tank
- The solar return-flow temperature drops further to below the storage tank temperature at the second inlet, and the return-flow is bypassed to the lowest inlet into the tank
- Under bright sunlight again, the space heating is turned on and the Thermo-Differential Valve directs the return-flow into the bottom inlet of the tank
- Domestic hot water consumption causes the storage tank temperature at the bottom space heating inlet to fall below the temperature of the space heating return-flow, which is therefore bypassed to a higher inlet into the tank
Besides directing the flow to different levels in a single storage tank, the Thermo-Differential Valve can also bypass a storage tank and direct the flow to a second storage tank, creating a stratified cascade arrangement of multiple storage tanks, and it can even bypass the storage system completely when no useful heat is available, and direct the flow straight to an auxiliary boiler.
The self-actuating technology (patent pending) of the actuator is based on mass-transfer inside the actuator, driven by vapor pressure differences, in response to one part of the actuator becoming warmer than the other, which makes it completely independent of the actual temperature of the water; it responds purely to temperature difference. As the liquid inside the actuator flows from the warmer section to the cooler section, there is a change in the buoyancy of the section that protrudes into the storage tank changes, which acts as a float when it is filled with vapor, but sinks when it is filled with liquid. This change in buoyancy of the float is what actuates the valve (with the buoyancy force amplified through leverage), the mechanism of which is illustrated by the animation below.
Click on the valve to see how it changes position in response to a change in temperature difference between process flow and storage tank
- Bypass position - the temperature of the fluid flow into the valve is lower than the temperature inside the storage tank, the fluid flow is directed through the bypass port
- The temperature of the fluid flow increases; as it surpasses the temperature inside the storage tank, the valve switches to its open position
- Open position - the temperature of the fluid flow into the valve is higher than the temperature inside the storage tank, the fluid flow is directed into the storage tank
- The temperature of the fluid flow decreases; as it falls below the temperature inside the storage tank, the valve switches to its bypass position
The interval of temperature difference in which the mass-transfer takes place is very small, typically around 1˚C, and outside this interval the actuation force remains almost constant, regardless of whether the temperature difference is 4˚C or 40˚C, which means the actuator can operate over a very broad temperature range. The straightforward working principle of the actuator, which does not require any springs, flexible membranes or seals (actuator completely made of stainless steel), makes the Thermo-Differential Valve extremely reliable and durable.
Benefits compared to traditional stratification approaches
Compared to a system using zone valves, the Thermo-Differential Valve offers:
- No controller, sensors or thermowells required
- Increased reliability; simple and robust design with no electrical parts
- No electricity consumption
- Very easy installation; no wiring, no controller setup
Compared to using a stratification diffuser, the Thermo-Differential Valve offers:
- Real increases in stratification due to the flow entering tank directly at the correct level, without loss of stratification due to tank water entering the diffuser (chimney-effect) and heat conduction between diffuser and tank
- Optimal stratification performance independent of flow rate, and of the temperature profile in the storage tank
- Suitable for applications with a variable flow rate
- The use of multiple layered storage tanks in series, and the ability to bypass tanks and go directly to auxiliary heater
The Thermo-Differential Valve has two basic configurations;
|TDV-C:||The flow enters the storage tank if its temperature is higher than the temperature in the storage tank (at the position of the float inside the tank), and bypasses the inlet when its temperature is lower.|
|This configuration is ideal for the flow adding heat to the storage tank (e.g. solar panel).|
|TDV-D:||The flow enters the storage tank if its temperature is lower than the temperature in the storage tank (at the position of the float inside the tank), and bypasses the inlet when its temperature is higher.|
|This configuration is ideal for the flow drawing heat from the storage tank (e.g. space heating).|
The valve actuates based on the temperature difference (ΔT = Tflow – Tstorage) being either positive or negative at the position of the inlet (with small offsets due to the float changing position as the valve actuates; this hysteresis prevents rapid switching of the valve around the point of zero temperature difference).
Benefits of Thermal Layering
The Thermo-Differential Valve enhances the performance and efficiency of thermal storage systems by directing the water flow to the most appropriate level of the storage tank, thereby creating and maintaining a high degree of thermal layering (stratification) in the storage tank of storage systems:
- where one of the flows into the tank is variable in temperature
- where multiple heat sources are adding heat to the tank at different temperatures levels
- where multiple flows, with different temperature levels, are drawing heat from the storage tank.
Thermal storage systems benefit from a high degree of thermal layering in the storage tank, because this prevents the heated water in the top of the tank from mixing with colder water below, which increases the output performance of the storage system, and it also prevents the cold water in the bottom from mixing with warmer water above, which increases the efficiency of heat sources such as solar, and also of condensing boilers.