Economiser
Also known as: economizer, economiser circuit, vapour injection (EVI)
Short definitionAn auxiliary circuit that cools the liquid once more ahead of the expansion valve and feeds the vapour produced into the intermediate port of the compressor. It adds capacity and efficiency at low temperature.
Screw compressors and vapour-injection scrolls have a second inlet that opens partway along the compression path. A small share of the liquid leaving the condenser is split off, passes through its own valve, evaporates in a plate heat exchanger and cools the main liquid by 15–30 K. The vapour goes to the intermediate inlet. The compressor compresses it from halfway, so the extra work is small, while the colder liquid reaching the evaporator carries more heat per kilogram.
It pays off in quotes for frozen storage and blast freezing: with evaporation between −30 and −40 °C, capacity rises by 20–40% and COP by 10–20%, while in chill rooms the difference stays small. A compressor one size smaller may then be enough. If the subcooled liquid pipe is not insulated, the gain is lost on the way. When the compressor steps down to low capacity, the intermediate inlet closes on most models, so capacity is checked for that condition too.