Typescript report written by A.S. Cromarty covering the research programme leading to the production of the ADDON Heat Recovery Unit for use in dairies. The report also 'describes alternative, simplified methods for determining performance under farm conditions.' Cromarty prepared the report when he was considering becoming a consultant on the installation and use of heat pumps on dairy farms. The document begins with an analysis of the performance of early bulk tanks submitted to the NIRD Test Facility for compliance with the Milk Marketing Board BC 56 Test specification.