Heat pumps offer superior energy efficiency compared to other methods of heating such as boilers, furnaces or electrical-resistance heaters. The “heat out” of a heat pump is typically several multiples of the “work in.” That’s because the “heat out” includes the energy “picked up” at the evaporator as well as the “work in” by the compressor. Consequently the coefficients of performance (COPs) for heat pumps are several multiples of one and can be quite high indeed depending on the design of the heat pump and the heat exchangers in the system.
MicroGroove further increases the COP of heat pumps in several ways. In the case of an air-to-air HP, the advantages are the same as for AC unit. In the case of heat pump HPWH, the unit will benefit from a MicroGroove evaporator. In both cases, MicroGroove heat exchangers offer high heat-transfer coefficients, more compact coils, and lower power requirements for fans.
Easy Drainage with RTPF Design
MicroGroove is especially competitive with MicroChannel in heat pump applications. That’s because a heat pump made with a round tube plate fin (RTPF) condenser and evaporator has no problem shedding condensate in either AC or HP mode of operation, unlike a MicroChannel heat exchanger. The “plate fins” of RTPF coils typically are oriented vertically so water drains easily from the top to the bottom of the sheets. In other words, the tubes penetrate the sheets at right angles and water easily flows around them.
The same holds true for RTPF coils made from smaller diameter copper tubes. There may be more tubes penetrating the plate fins but water flows easily around the smaller diameter tubes. The open structure of RTPF design is a major advantage of MicroGroove heat exchangers compared to aluminum microchannel heat exchangers. That’s why MicroGroove heat exchangers are commonly used in the outdoor evaporators of heat pumps especially in colder climates where frosting may be an issue.
A Myriad of Products
Smaller-diameter, inner-grooved copper tubes can be found in the heat exchangers of a myriad of heat-pump products. Commonly referred to as “MicroGroove coils,” these advanced heat-exchangers are well suited for use in heat pumps.
They are more efficient and more compact and contain a smaller volume of refrigerant compared to earlier generations of coil designs. MicroGroove coils are suitable for refrigerant-to-air heat exchangers, including evaporators and condensers as well as gas coolers.
Many examples already exist of MicroGroove coils in diverse products such as clothes-drying heat pumps and heat pumps for residential heating and cooling. Once the smaller-diameter copper tubes are interlaced with aluminum fin plates and mechanically expanded, the ruggedness of the resulting round tube plate fin (RTPF) heat exchangers is remarkable.
Possible candidates for adopting MicroGroove technology in heat pump applications include the following:
• Residential HP for space heating and cooling
• Residential HPWHs
• Commercial HPWHs
• HP with eco-friendly refrigerants
• HP with natural or chemical-free refrigerants
• HP with phase-change materials
A hot water heat pump (HWHP) typically includes a heat exchanger for the evaporator, which collects heat from ambient air sources; and a heat exchanger either wrapped around the outside of the water tank or submersed inside the water tank. For HWHPs, smaller diameter tubes make sense only if multiple tubes are used in parallel, to alleviate the higher pressure drop of smaller diameter tubes in long lengths.
Technical Paper at IEA Heat Pump Conference
Yoram Shabtay presented a paper titled “Advanced round-tube, plate-fin (RTPF) heat-exchanger coils contribute to the high efficiency of heat pumps” at the Twelfth International Energy Agency Heat Pump Conference (IEA HPC) which recently held in Rotterdam, The Netherlands, in May 2017.
Previously, Professor Guoliang Ding presented a technical paper at the Eleventh (IEA HPC) in Montreal, Canada, titled “Experimental investigation and structure optimization of distributors used in heat pump air conditioner with microgroove tubes.”
The website www.microgroove.net includes additional Q&A’s relating to heat pump technology. It also includes links to the MicroGroove series of webinars. A technical literature section provides links to technical papers relating to laboratory experiments, tube circuitry optimization, fin design and manufacturing equipment. A special landing page has been established with the focus on the heat pump applications of MicroGroove technology. http://www.microgroove.net/heat-pumps
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