Impact of Energy Efficiency Improvements on Water Heating Costs on New Zealand Dairy Farms Dale Eastham – P G Dip candidate

Summary

This project is one of five projects of an energy assessment programme.

During this research project data will be collected from several milking sheds, including Massey’s number Four Dairy Farm. The data will be analysed to determine how much electricity is used to heat water used in the shed.

Three methods of reducing the amount of power required will be assessed.

 Batch heating   Timer installation to control when water is heated Re-routing excess heat energy (theory or practice)

Situation

Dairy farms are heavy consumers of electricity. Most electricity is consumed in the dairy shed by vacuum lines, milk chilling, water heating, and pumping milk and water.

These activities consume varying proportions of power depending upon the system design of the milking operation. On Massey’s Number Four Dairy farm, water heating consumes 25-30% of the electricity use alone.

There are many ways of reducing the amount of electricity consumed to heat the water needed on a daily basis. However, finding a method that is cost-effective, practical for a dairy shed situation, and has an acceptable payback period for the farmer is difficult. Little work has been done previously on developing systems for helping the individual dairy farmer to solve these problems.

Project Aim

 To report on the energy requirements of alternative cost reduction methods to water heating in dairy sheds.

Objectives

 Install data loggers to record the amount of electrical power used in Massey’s number Four dairy farm for hot water heating.

 Collect, interpret and report on the data from the loggers installed on the relevant machinery.

Hypothesis

 Savings will be achieved by only heating the amount of water required for operating the dairy.  Savings will be achieved by installing a timer on the heating element will eliminate ‘maintenance heat’ requirements.

 Savings will be achieved by modifying the shed’s systems to allow excess heat energy to be re-used in other systems around the shed.

Methodology

Data recorders have been placed in several dairy farms around the Manawatu since the past summer.

Loggers are attached to selected appliances to measure and record the electricity used.

The water heating data from these loggers will be evaluated and the system modified and the data will be recorded for another four weeks and then reviewed again.

Hot water tank temperatures (76 days)

60 50 40 90 80 70 30 0:00 2:00 4:00 6:00 8:00 10:00 12:00

Time of Day

14:00 16:00 18:00 20:00 22:00 0:00

Limitations

 Budgetary constraints - some machinery that could be useful is currently hugely expensive (Mohana Blue and DTS).

 Time constraints - deadlines set down by the projects financial backers.

Continuous Heating- the present situation

 After a hot wash cycle no more hot water is immediately available for extra washing.

 Installing a timer controlling when water is allowed into the cylinder via a solenoid would solve this problem by acting as an indirect heating element control timer.

 This creates a batch-heated, drain-down hot water system, opening up various heat recovery and timing options.

Waste Heat Recovery

Waste water is put through heat exchangers once prior to dumping it.

 Warm water is circulated slowly through exchangers (requiring separate pump and storage tanks).

4 Main sources for recovering waste heat energy have been identified

 Warm milk en route to the storage vats  Vacuum pump discharge air  Hot-wash waste water  Milk chilling equipment

Warm Milk Heat Recovery

 2-3 times the volume of warm milk as volume of hot water needed is available, meaning there is sufficient heat energy in the system.

 But this heat is only available before hot water is needed.

immediately  This could necessitate storing the hot water until the next milking, meaning additional costs.

Vacuum Pump Discharge Air Heat Recovery

 Could be put straight into a heat exchanger but using a heat pump first to concentrate the heat energy would be needed to take full advantage of this source.

 Even so, it would still be subject to the same timing problem as before.

Milk Chilling Equipment Heat Recovery

 Waste heat source with the most potential.

 Heat will be taken from the refrigeration unit by a desuperheater e.g. DTS, Mohana Blue.

Regardless of method, energy input is needed to raise the water temperature  These methods lead to a significant reduction in energy input costs needed for water heating.

 Shifting the heating load to night time electricity rates has the potential to halve this cost again.

 Additionally, delaying the heating process to just before milking will eliminate maintenance heating costs and losses.

Other possible measures

 Using one large tank sufficient for the entire days’ hot water needs would lose less heat through irradiation than multiple, smaller tanks.

 Insulating the hot water cylinders in any way would further reduce heat loss.

Supervisors

Chief Supervisor: Prof. Ralph Sims Co-supervisor: Karl Hartman