Technical
TXV , EEV AND PWMS
By Ben Sieweke , CST manager and IoT at Carel Controls South Africa
I don ’ t know what you think , but it seems that in today ’ s language , the term technology is always associated with speed .
All images by Carel Controls South Africa
Communication speed and high-speed control are concepts
– and just like in the general meaning – refrigeration and air conditioning applications are also synonymous with value and objects and / or services that users are willing to pay more for than competing products with lower performance and / or quality .
In other words , technology is something that ‘ counts ’, as it offers advantages over cheaper solutions that would otherwise not be distinguished from the competition . So , how can the value of a certain product and / or service be understood when this does not simply depend on the commonly-accepted concepts of value as described above , or cannot be conveyed by a brief advertising message ? I believe that electronic expansion valves ( EEV ) are a perfect example of this .
EEVs as they are commonly called , in fact , ensure far superior performance to traditional thermostatic valves , as they not only manage the actual expansion process , but also modulate the flow-rate based on the different parameters and needs that are defined in real-time based on information that is continuously acquired .
The working principle of an electronic expansion valve ( EEV ).
As a result of these capabilities , EEVs are the most advantageous solution , adding value in terms of energy savings in both the immediate and long term , and thus savings in total operating costs .
Indeed , the use of an electronic valve can save an estimated
5 % a year without any other changes to the circuit , and up to 30 % when used on a heat pump with a brushless direct current ( BLDC ) inverter compressor .
Furthermore , through the combination of electricallycontrolled movement and smart control algorithms , EEVs can work at very high speed , allowing extremely rapid responses to any transient conditions . Certainly , the best electronic valves can cover the entire stroke in a very short time ( around 3 seconds ), approaching the closing speed of a solenoid valve , which consequently is no longer needed .
Another major benefit compared to traditional thermostatic valves is the ability to manage a very wide range of refrigerants without any modifications , other than configuring the driver , thus making them ideal for refrigerant retrofits in the field subsequent to system commissioning .
EEV technology is positively impressive when described this way : it makes a concrete contribution to improving our lifestyle , helping us save energy and reducing our impact on the environment we live in .
Following the minimum safe superheat from an evaporator coil we can note that the demand is not a linear request but that of a curved graph . The operations of a thermostatic expansion value ( TXV ) relate in a linear graph leading to areas of missed opportunity where energy savings and thermal performance can be improved .
The other danger of this is if the TXV were to have its superheat set outside the minimum safe superheat , we are at risk of operating at a lower superheat during the pull down for a fridge .
Following the minimum safe superheat from an evaporator coil we can note that the EEV can obtain and maintain the minimum safe superheat throughout the operation of the evaporator coil .
This simply maximising the available cooling available
www . hvacronline . co . za RACA Journal I January 2021 71