Which TRV?

Which TRV?

Properly selected and installed, TRVs are proven to provide accurate temperature control in individual rooms, reducing heating costs and enhancing comfort. However, not all TRVs are the same, as Bjorn Sejr Nielsen, Marketing Director of Danfoss, explains.

Independent research
Invented by Danfoss back in 1943, radiator thermostats (TRV) remain essential to achieving the optimum efficiency of most ‘wet’ domestic central heating systems. This claim is supported by heating control tests carried out in the Energy House at Salford University. The results highlighted the importance of TRVs to ensure satisfactory heat distribution around a dwelling. Indeed, the university’s research showed that this is not possible without TRVs, even if the system is balanced.
Although the TRV has become one of the most widely-used heating controls the extensive range of products now available, all offering different features, functions and sensors, can be confusing for even the most experienced heating installer. Making the right choice for the end-user’s needs, rather than simply sticking with what you know or picking the cheapest option, can be key to keeping customers happy and securing new and repeat business.

Pros and cons
If you take a look through any of the online plumbing forums you are likely to come across discussions about which TRV to install and the perceived pros and cons of different brands and types. To assist selection, I believe installers need to be aware of what is arguably the most critical difference between the various TRVs on the market and that’s the material used in the sensor.

Basic concept
Let’s start by outlining the basic concept behind the modern TRV. Inside each TRV head is a sensor containing a material, usually wax or a liquid, which expands as the room temperature warms up and contracts when it cools down. The sensor is connected to a valve seat inside the body, which opens as the sensor contracts and closes as the sensor expands to allow more or less water through. Whilst this concept is in itself very effective, the material used inside the sensor will affect the TRV’s overall performance and accuracy. This is because different materials have different thermal properties, initially and over time.

Response time
According to the basic laws of physics, the lighter the material used in the sensor the quicker it will respond to changes in the ambient temperature. With this scientific principle in mind, it is fair to say that liquid models have the advantage of a faster response time compared with a wax-filled sensor. Because wax is a heavier, denser material it is relatively slow to expand or contract. You don’t need a science degree to tell you that when it comes to heating your home, the TRV’s response time will have a direct impact not only on comfort but also on energy consumption and overall heating costs.

Wax-filled TRV
Apart from a slower reaction time to changes in room temperature, the wax in a TRV sensor has, in many cases, a tendency to change consistency over time. This is primarily due to the crystalline composition of wax. The crystals become bigger with constant expansion and contraction. This makes the wax harder and heavier so it needs a higher temperature to react. Whilst this process may take up to a year, during that time the end-user will find they are having to increase their temperature settings in order to achieve the same level of comfort. Making this incremental adjustment over time can make a big difference to heating costs and may ultimately negate the potential energy savings of installing TRVs. On top of all this, the installer could be faced with a costly call-back from a dissatisfied customer, something that every reputable business tries hard to avoid.

Informed choice
TRVs are proven to help households save energy and improve comfort but in order to maximise these benefits over the longer term it is important to know what’s inside the sensor. When you know the differences, you can make a more informed choice for your customer and help maintain the TRV’s rightful reputation as a cost-effective, energy saving heating control. If you are in any doubt, you can always check out the various options on manufacturers’ websites or just ask your supplier’s advice before you buy. For more information visit