Cold-climate R290 heat pump achieves reduced refrigerant charge with 5mm tubes
Israeli heat-exchanger manufacturer Lordan Coils has developed a cold-climate propane (R290) residential heat-pump water heater (HPWH), using 5mm (0.2in) MicroGroove copper tubes to achieve a low charge.
The MicroGroove 5mm copper tubes are used to create bent L-shape heat exchanger coils with high heat-transfer coefficients, resulting in higher seasonal energy efficiency ratios (SEER). The small diameter tubes mean less material is needed, giving lower system weight while maintaining the same capacity, according to Yoram Shabtay, President for U.S. consulting firm Heat Transfer Technologies and Peter Mostovoy, Business Development Manager at Lordan.
“It’s very clear to see that the output – in terms of watts per volume – you can get much more output by putting it together in 5mm,“ said Mostovoy.
Anticipating queries about the alternative use of microchannel technology, he added, “It has to drain, it’s getting wet all the time, it’s outside, it’s dirty, the microchannel doesn’t do it, and it’s hard to bend.”
The goal when designing the air-source R290 HPWH was to achieve 20kW of heating or 14kW of cooling (5.7TR heating/4TR cooling), which is enough for a standard house, according to Mostovoy. The smaller diameter tubes mean that the charge for the unit is 0.519kg (1.14lbs), compared to to 1.64kg (3.6lbs) for a similar capacity system with ⅜in (9.5mm) tubes. To those arguing that this charge is still too much, Mostovoy said “don’t forget that this [monoblock] unit sits outside the house, heating a water-glycol mixture, and that mix is what’s going into the house, so the charge is all outside.”
In addition, the reduced need for material means that the weight of the tubes in the tested system goes down from 23.5 to 11.5kg (51.8 to 25.4lbs), when compared to traditional ⅜ in tubes, and as everyone knows “copper prices are going through the roof,” Mostovoy noted.