How Heat Recovery Works

A refrigeration system works by transferring heat from one place to another. In a bulk milk cooler, the refrigeration cycle extracts heat from the milk and rejects it to the surrounding air through the condenser. In a standard installation without a heat recovery unit, this heat is simply expelled to the atmosphere — wasted energy that represents a significant operating cost opportunity.

The heat recovery unit (HRU) intercepts this rejected heat before it reaches the air-cooled condenser and uses it to heat water in an insulated storage tank. The principle is thermodynamically elegant: you are using the same energy input to cool the milk and simultaneously heat water, effectively getting two useful outputs from one power input.

Quantifying the Energy Savings

The energy savings from an HRU are substantial and directly calculable for any installation. In a dairy operation cooling 2,000 litres of milk per day, the refrigeration system rejects approximately 2.5 to 3.5 kWh of heat per 1,000 litres cooled. This heat, if captured, is sufficient to raise approximately 200–400 litres of water from ambient temperature (25°C) to 65°C.

For a dairy operation requiring 300 litres of hot water per day for udder washing, CIP cleaning and general farm use, the HRU typically eliminates 80–100% of the water heating energy requirement during peak collection seasons. The annualised energy savings translate to a financial saving that recovers the cost of the HRU within 12 to 18 months in most installations — after which the unit generates pure cost savings for its remaining operational life of 15+ years.

Applications for Recovered Hot Water

Hot water produced by the HRU can be used across a range of dairy farm and processing applications. For farm-level dairies, the primary use is pre-milking udder preparation — warm water washing significantly reduces bacterial contamination of the teat end and improves milk let-down. CIP cleaning of the bulk milk cooler tank and associated pipework requires hot water at 65–80°C; the HRU can supply this at the required temperature with appropriate system design.

For processing operations, hot water from the HRU can pre-heat process water before it enters the pasteuriser, reducing pasteuriser energy consumption. In Novalac-type all-in-one processors and milk heating vat applications, the HRU provides a low-cost heat source that significantly improves overall system efficiency.

Specifying the Right HRU for Your Installation

The HRU is sized based on the BMC compressor capacity and the daily hot water requirement. ADFPL manufactures HRUs in the 200L to 700L storage capacity range, matching the full range of our bulk milk cooler product line from small village-level units to large plant installations. The HRU includes an insulated AISI 304 stainless steel or food-grade polymer water storage tank, a heat exchanger coil connected to the refrigeration circuit, and thermostatic controls to maintain water temperature at the desired setpoint.

The HRU is compatible with all ADFPL bulk milk cooler models and can be retrofitted to existing installations. For new installations, integrating the HRU from the outset is always preferable to retrofit as it allows the refrigeration pipework to be optimised for HRU integration.