Introduction to VRF systems

Recently, there has been an Asian invasion of America.




Asian variable-speed heat split heat pump systems, that is.

While most engineers and contractors are familiar with the now-common ductless mini-split systems, these systems have a bigger cousin which can match multiple outdoor condensers with multiple indoor fan coils using variable speed compressor technology to greatly improve efficiency and add significant zoning flexibility to building designs.




Davis Watkins, Vice President of Applied Systems, Sanyo HVAC Solutions, recently wrote an introductory article for HVAC insider describing these systems, their applications and installation. He also debunks several myths about these systems that have caused concern in the past. It is well worth a read to understand how these systems provide better comfort control with great energy savings. A copy is locate here: Ductless Split System Technology: From Bonus Rooms to Commercial Buildings

Personally, I think one very strong argument for these systems can be summed up in a single graph:



This is a chart of the heating performance of the Sanyo ECO-i VRF system at low ambient conditions. Note that at as low as -4 deg F, the ECO-i VRF system still provideds 60% of the rated heating capacity without supplemental strip heat. Keep in mind that in a heat pump system the rated heating capacity is usually about 30% or so greater than the rated cooling capacity. In other words, you will get nearly 12 tons of heating out of a 12 ton cooling unit even in sub-zero weather!

If you are interested in reducing your carbon footprint, moving to a fully electric heat pump system makes sense in a primarily hydroelectric utility market--and even more so if you don't have to size your electrical service to provide redundant electric strip heat! Or, for that matter, pay for the energy required to provide that strip heat.

Another feature that highly recommends these systems is the capability to provide heat recovery while operating in simultaneous heating and cooling mode. A three-way Sanyo ECO-i system can operate much like a water-source heat pump system, re-using heat rejected from warm interior zones at perimeter zones that require heating. This inherent energy recapture ability allows the compressor in the outdoor unit to only have to work hard enough to transfer the difference in capacity between the two modes. If, on a given system, you have 7 tons of heating load and 4 tons of cooling load (11 tons, total) the compressor actually only sees 3 tons of load!



These advantages are above and beyond the already impressive efficiencies gained by the use of variable-speed compressors, and transferring heat and cooling energy with efficient refrigerant transfer instead of much less efficient air transfer. And, of course, these systems can offer great architectural advantages too: Lower floor to ceiling height, smaller spaces with independent comfort zones, very easy reconfiguration, etc.

It's no wonder these systems are gaining traction in a big way in the North American market.