Heat Pump Thermal Transfer Fluids. John's FAQs

Renewables expert, John Westerman understands Ground Source Heat Pumps, the importance of using quality thermal transfer fluids and getting the installation right.

Here are some Frequently Asked Questions that John has answered and may help you or your customer in maximising the performance of their Heat Pump system.

Q. My Heat Pump installation is malfunctioning, and after a few hours running the yield drops.  Why is this?

John:  There are two possible explanations:

1) The frost protection temperature of the Thermal Transfer Fluid (TTF) is too close to the operational design temperature.  As it approaches its protection point, the TTF undergoes significant increases in viscosity and "layers" of the TTF may stop flowing freely.  The heat exchange drops and the fluid slowly freezes in the heat exchanger.  The freezing point of the fluid must be at least 5 degrees lower than the lowest temperature likely to be reached in the exchanger.

2) The circuit contains debris or tartar.  This ‘sludge’ will settle in the areas where there are the greatest losses of load and the coldest areas, so generally in the exchanger.  The only options are to either drain and clean out the system, or to mount a bypass filter to remove the sludge. 

Q. I want to top-up the thermal transfer fluid in the heat pump system which already contains a fluid, the source of which I do not know.  What should I do?

John:  Fluids of the same chemical base are generally miscible, meaning that if you mix them you get a homogeneous solution, unless they are thermal transfer fluids using different glycols (MEG, MPG etc).  However, this doesn’t mean that the fluids are compatible.  Two different fluids will have different formulations in terms of corrosion inhibitors.  Mixing them together may result in a blend of corrosion inhibitors, the effectiveness of which cannot be determined.

Before adding anything, we recommend that you check the existing solution in the circuit to ascertain whether it might be better to undertake a complete replacement of the fluid.

Q. I want to add treatment chemicals into my heat pump collector. Should I?

John:   The fluid you use will have undergone a series of development studies designed by the manufacturer.  Its corrosion inhibitors will have been assessed and validated through a number of corrosion tests.  Therefore, there is no need to add other products.  Furthermore, the addition of other products could destabilise the formulation of the Thermal Transfer Fluid and reduce the effectiveness of the corrosion inhibitors in the system.

Q. I would like to know the lifespan of the thermal transfer fluid in my installation.  Is this possible?

John:   Unfortunately, it is impossible to give a specific duration. This is because the corrosion inhibitors will be "consumed" at varying speeds over time according to the preparation and installation procedure, operational constraints, the kinds of materials, the extent of galvanic coupling and so on.  Only an analysis of the Thermal Transfer Fluid can determine whether you need to renew it.

Q. I put red thermal transfer fluid in my system and the liquid is now a different colour.  Is this a problem?

John:  The dyes used in thermal transfer fluids are organic molecules.  The coloration can change under the influence of the temperature or the metal oxides present in the circuit.  This colour change does not necessarily mean that the product is no longer effective.  We recommend that you test for performance indicators.  Please also read the question about using pure glycol/thermal transfer fluid below.

Q. I want to use a pure glycol/thermal transfer fluid because it is cheaper.  Is this OK?

John:   A word of caution: pure glycol contains no corrosion inhibitors. 

Using this kind of product in aqueous solution may cause severe corrosion to your circuits.

Even if the pipes are made of plastic or stainless steel, if you have a different alloy somewhere in the system (eg copper in a heat exchanger), you will encounter galvanic coupling and we do not know in this case which alloy will act as the shield to the other.

Q. What if I want to buy the thermal transfer fluid as a concentrate and dilute it myself?

John:   We recommend using de-ionised or demineralised water in order to limit the introduction of compounds (for example chlorides, sulphates and carbonates) that can form sludge and may jeopardise corrosion resistance.  All the standardised corrosion tests are carried out with concentrations of 33% by volume of the thermal transfer fluid.  Below this concentration, the amount of corrosion inhibitor in the circuit could be too low and may not provide adequate protection against corrosion.

Q. Can I use galvanised steel for my pipes?

John:   Be warned that while the zinc in galvanised steel protects the steel from corrosion in a wet atmosphere, zinc is incompatible with glycols.  Galvanised steel will be "stripped" by the glycolated water and a very sticky sludge (zinc salts) will settle, often clogging the heat exchanger or filters on the system.

Climalife is on hand to help you with any upcoming projects or questions of your own.

Why not get in touch on 0117 980 2520 or climalife.uk@climalife.dehon.com .

Information on the Climalife Renewables product range can be found here.

Read John's 7 thinks to consider when selecting a Thermal Transfer Fluid