New PBF technology has potential to eliminate scaling in CO2 heat pumps

By team, Jan 19, 2015, 10:44 7 minute reading

In response to the need to reduce maintenance costs and improve efficiency in conventional domestic hot-water heat pumps, the brain trust at QSBR Innovations (QSBRI) Ontario, Canada, are introducing their patented Passive Back Flow (PBF) technology to the market. In an exclusive interview with QSBRI’s Dr. Steve Harrison and Managing Director Robert Stinson, finds out more about PBF technology and its potential to transform the transcritical CO2 heat pump market.

PBF technology

The passive back-flushing system is designed to protect heat exchangers, condensers or gas coolers used in typical water heating applications. Installed on the water supply to the unit, it allows the unit’s heat transfer device to be routinely back-flushed many times a day as hot water is consumed. The action is a normal operation of the system and does not require user intervention, external power or controls to function. The PBF device has the potential to drastically improve long-term performance and life cycle, while reducing maintenance costs.  It also enables the reliable use of compact high-performance plate-style condensers and gas coolers potentially reducing overall system dimensions and cost.  

Potential to eradicate scaling

In December, QSBRI completed tests on a trans-critical CO2 heat pump water heater-fitted with two different style gas coolers; one used a typical ‘spiral’ unit used by the industry (commonly used in Japanese CO2 hot water heat pumps) and the other was a brazed-plate design operating under natural convection operation. Using accelerated testing, the PBF valve was shown to completely protect the brazed-plate gas cooler, while the spiral gas cooler fouled to point that water circulation ceased and heat transfer was drastically reduced. Adhering to new European hot-water draw standards, these test conditions presented significant challenges to the PBF technology, but QSBRI found the results to be consistent with earlier tests and field experience on brazed-plate heat exchangers in solar water heating systems, which also showed no instances of fouling. How is this technology able to more effectively mitigate the detrimental effects of scaling and fouling in heat exchangers than conventional solar charging systems?

Dr. Steve Harrison: We know with large commercial systems it’s common to perform regular maintenance on the heat exchanger, where you back-flush the heat exchanger to push out any solids or dirt. The problem was trying to translate that into a residential situation with smaller heat exchangers, particularly with brazed-plate heat exchangers, which are low cost, highly efficient and compact, but generally have small flow passages. What we sought to do was implement a system where every time the homeowner draws water out of their system, every time they open their tap, cold water flows into the heat exchanger at a point above the heat exchanger and reverses the flow into the heat exchanger. What that does is it introduces colder water in the passages and scours the surface, dissolving the minerals and blows out any deposits. The key feature that makes this unique is it is passive, so in effect every time the homeowner goes to use their hot water they’re servicing their heat exchanger, which basically protects it from fouling over the life cycle of the appliance. It’s very simple to implement and has proven to be highly effective. There are literally thousands of solar versions of these operating in North America, all the way from Florida to Alaska, and there have been virtually no instances where we’ve had any issues.

Robert Stinson: We estimate that approximately 50-60 percent of the world experiences hard water conditions, where it’s over 120mg/litre of calcium carbonate and other inverse soluble salts that scale components and reduce heat transfer capability, so there’s quite a demand for this type of technology. What excites you most about this PBF technology and what impact do you think it will have on the CO2 transcritical heat pump market?

Dr. Harrison: We’ve known for quite a while that there are lots of applications for this technology and we know that hard water quality issues exist around the world. We know in particular that heat pumps are a growing area, especially CO2 heat pumps, with all of the concern with traditional refrigerants and climate change, there is a lot of motivation to move to these natural refrigerants. The CO2 heat pump is an excellent application for this technology given the working environment of high pressures and temperatures. We’re really excited about this particular technology because it can be applied to a number of existing platforms, they don’t have to be CO2, but certainly the application on a CO2-based heat pump is very promising. You’ve been testing since November 2013, what results have you uncovered and have they exceeded expectations? 

Dr. Harrison: So far we feel we have basically eliminated the potential for scaling in the heat exchanger. We have done an extensive amount of testing in the field, accelerated testing in the lab, and so far we are able to keep the heat exchangers free of fouling. We don’t claim to be able to take a completely fouled heat exchanger and reverse the process, but if a PBF valve is installed by the manufacturer or at the time of installation, we don’t anticipate any degradation in the heat exchanger performance or any build up of scale over the life of the appliance. What will be the main benefits of this technology for end users and home owners?

Robert Stinson: For a customer there are huge advantages because you’re not going to incur maintenance costs, you’re not going to have a plumber come out because your hot water has run out or your electricity bill has gone up because the heat exchanger on your hot water system has fouled. From a manufacturer’s point of view, the PBF technology is very advantageous because you can either lower the cost of your appliance or increase your margins because you’re significantly reducing your space requirement, the weight, and the overall cost of the heat exchanger. Is this technology specifically targeted at the residential market?

Dr. Harrison: Our initial focus is on the residential market because this is the market which does high volume and has less opportunity to have a scheduled maintenance regime. However PBF has been used in commercial settings in the past and we are developing valves to meet the commercial market demand. The CO2 heat pump market is growing in Europe and is already huge in Japan, with roughly four million CO2 heat pumps installed. What plans do you have for these regions?

Dr. Harrison: Essentially, this technology should be widely used; certainly heat pumps are heavily marketed in Japan and Korea. There are very large numbers of these heat pumps being sold and they’re starting to be introduced in Europe. We’ve had a look at the effects PBF has had on the CO2 heat pump and the results have been very, very promising. The performance so far looks great. Spotted through Europe are areas that have very hard water conditions so we see lots of applications for this technology in Europe. We want to enable this technology, we want to see it spread, and we think we have the key to making the CO2 domestic hot water heat pump become a viable product in a wide range of geographic areas where hard water conditions can be overcome. Thank you Stephen and Robert for your time and good luck!


QSBRI is a subsidiary of Queen’s University’s Department of Mechanical and Materials Engineering where Dr. Steve Harrison operates the Solar Calorimetry Laboratory. QSBRI was originally founded by Dr. Harrison and his partners to commercialise technology developed in the laboratory.  With managing partner Robert Stinson and son Benjamin Stinson, QSBRI’s director of product development and marketing, the team has been busy running extensive tests on the application of PBF technology in transcritical CO2 heat pumps over the past How is this technology able to more effectively mitigate the detrimental effects of scaling and fouling in heat exchangers than conventional solar charging systems? How is this technology able to more effectively mitigate the detrimental effects of scaling and fouling in heat exchangers than conventional solar charging systems?


By team (@r744)

Jan 19, 2015, 10:44

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