Floating head pressure control
Also known as: floating condensing, floating condensing pressure, variable head pressure
Short definitionA control that does not lock the condensing temperature at one setting but follows the outdoor air and pulls it down. The compressor does less compression work and annual electricity consumption falls by 10–20%.
In an old-style panel the fans hold condensing at around 40 °C in winter too. Yet when the air is at 10 °C the same condenser can bring condensing down to 20–25 °C. With floating control the target is recalculated all the time as 8–12 K above the measured outdoor temperature. For every 1 K that condensing drops, the compressor draws 2–3% less electricity; the gain is larger in inland regions with cool nights and long winters.
The project needs an outdoor air sensor, a pressure transmitter on the discharge line and variable-speed fans, preferably EC. Condensing cannot be lowered without limit. A thermostatic expansion valve cannot feed the evaporator once the pressure difference shrinks, so condensing is not taken below 25–30 °C; with an electronic valve the limit becomes 15–20 °C. Hot gas defrost and the compressor’s operating envelope affect the limit too. Where there is heat recovery, the priority between the two is chosen by season.