Defrost control system for a refrigeration heat pump apparatus

In a control system for refrigeration heat pump having an outdoor coil through which air is blown by a fan for extracting heat from outdoor air and defrost means to periodically heat the outdoor coil to remove the frost comprising,

• condition responsive means adapted to respond to a condition indicative of frost formation on the outdoor coil,
• space temperature responsive means adapted to control the refrigeration heat pump upon a need for heat in a space,
• time controlled means adapted for periodically allowing the heat pump to operate upon a call for heat, by said space temperature responsive means, a predetermined total time period sufficient to bring about the frosting of the outdoor coil under predetermined outdoor ambient air conditions and thereafter initiate operation of said defrost means, whereby a value of said condition is measured at the end of said total time period,
• memory means for maintaining said value of said condition at the end of said predetermined total time period, and
• control means connected to said space temperature responsive means adapted to control the heat pump between said periodic time controlled operations for operations for a second total time period extending until said condition responsive means responds to said value of said condition and thereafter operate said defrost means to remove the frost from the outdoor coil.

In a defrost control system for refrigeration apparatus having an heat exchange coil through which air is blown by a fan for extracting heat from air and defrost means to periodically heat the coil to remove the frost comprising,

• pressure responsive means adapted to respond to an air pressure indicative of a predetermined restriction of air flow through the coil,
• time controlled operation means adapted for periodically operating the refrigeration apparatus for a predetermined total time period controlled operation sufficient to bring about the frosting of the coil under predetermined ambient conditions and thereafter operating said defrost means, whereby a value of said air pressure indicative of a predetermined restriction of air flow is measured at the end of said time period,
• memory means for maintaining said value of air pressure at the end of said predetermined total time period, and
• control means adapted to control the refrigeration apparatus and the defrost means between said periodic total time controlled operations for normal air pressure controlled operations for new time period extending until said air pressure reaches said value before the defrost means is operated to remove the frost from said coil.

In a control system for refrigeration heat pump having an outdoor coil through which air is blown by a fan for extracting heat from outdoor air and defrost means to periodically heat the outdoor coil to remove the frost comprising,

• condition responsive means adapted to respond to a condition indicative of frost formation on the outdoor coil,
• space temperature responsive means adapted to control the refrigeration heat pump upon a need for heat in a space,
• time controlled means adapted for periodically allowing the heat pump to operate upon a call for heat by said space temperature responsive means a predetermined total time period sufficient to bring about the frosting of the outdoor coil under predetermined outdoor ambient air conditions, whereby a value of said condition is measured at the end of said total time period,
• memory means for maintaining said value of said condition at the end of said predetermined total time period,
• defrost control means for initiating a defrost cycle at the termination of said total time,
• means for terminating said defrost cycle after a predetermined time of operation,
• control means connected to said space temperature responsive means adapted to control the heat pump between said periodic time controlled operations for operations for a second total time period extending until said condition responsive means responds to said value of condition before the defrost means is operated to remove the frost from the outdoor coil, and
• means responsive to said predetermined time of operation whereby if said time is greater than a selected time, said second total time period is reduced.