SPONSORED BY
HEAT PUMP GUIDE
Reversible propane air-to-water heat pump range
HKS Lazar, a manufacturer located in Jastrzębie-Zdrój in southern Poland, has developed a range of reversible propane (R290) air-to-water heat pumps with reduced refrigerant charges of less than 2.5kg (5.5lbs), and high COPs of up to 4.78
D
uring a three-year R&D project, the company focused on developing new types of evaporators and refrigerant separators, as these are the “two key factors to
improving COP when working with propane,” according to Paweł Matusiak, consultant with HKS Lazar. Mr Matusiak, and his colleague Martin Lazar, presented their results during the ATMO/DTI online conference, which took place on June 23-24. One of the issues the company needed to address was the fact
that “propane expands very quickly inside the evaporator tubes, which slows down the heat transfer,” Mr Matusiak said, adding that “you need an even flow of refrigerant” to optimise efficiency. HKS Lazar solved this by adapting its evaporator tubes with internal 3D modifications, resulting in a 50% reduction of the evaporator’s inner volume. “Inside the evaporator tubes exist several ring chambers where refrigerant flows very close to the tube edge with different speed and expands slower,” Mr Matusiak explained.
Mr Matusiak said this new type of evaporator is for “wet”
evaporation and described it as something between flooded and DX. As an example of the reduced volume, he described a unit with a 9kW (2.6TR) of cooling capacity, but instead of a standard 6ltr (1.6gal) volume evaporator, HKS Lazar’s new prototype only has a 3ltr (O.8gal) volume. The 3D modifications and the addition of grooved copper
tubes, meant that Lazar now has “better performance, but the active surface is the same,” Mr Matusiak said.
Inside the evaporator tubes exist several ring chambers where refrigerant flows very close to the tube edge with different speed and expands slower – Paweł Matusiak
www.heatingandventilating.net Controlling air flow
The HKS Lazar team also noticed that when working with R290, you have to pay particular attention to disturbances in air flow. They thus came up with a novel solution of externally controlling the air flow. Having found that evaporators with horizontal or vertical fan positions negatively influence the air flow velocity, due to different pressure drops, the team devised an L-shaped evaporator divided into three sections (upper, middle and lower). These sections each have segments with differently spaced fins to make corrections to the air flow, solving the problem and improving the air flow. Lastly, for the R290 evaporators, the team looked at oil
return, particularly foaming lubricant and lubricant solubility. A new circuit design using gravity ensures the oil returns smoothly, with no leftovers remaining in the evaporator during long-term work. The HKS Lazar team didn’t just look at evaporator
improvements though; they also looked to improve their refrigerant separator. They designed a new tubular solution that can achieve low superheat while reducing the risk of compressor damage, reduce or control the compressor temperature and eliminate the need to shut off the compressor during the defrost period. The team has nicknamed this solution “spider”. After a 6,000-hour test of a 20kW (5.7TR) heat pump,
HKS Lazar concluded that the evaporator experienced even freezing of all rows and it achieved an improved defrost period with less energy, guaranteed oil recovery during low refrigerant flow and most importantly, no signs of compressor damage. All of this led to an increased COP. You can view HKS Lazar’s conference presentation with
more detailed data sheets
https://atmo.org/atmo-dti-2020- technical-session-small-scale-1-day-2-24-june/
October 2020
35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
