Objective
To demonstrate the reduction in refrigeration costs in a lager brewery, by the incorporation of a 10 MW Thermal Store at -10 deg. C to satisfy a two tier temperature regime normally at -8 deg. C, and -12 deg. C, but elevated to -3 deg. C and -7 deg. C, to save in higher evaporating temperatures. Additionally the condensing temperatures will be lowered from 35 deg. C to 28 deg. C by day and 23 deg. C by night.
The 10 MW Thermal Store will reduce the peak demand for cooling by over 60% and reduce the electrical consumption of the compressors by 33%.
The Thermal Store uses hydrated salts in a phase changes made to store energy using the cheaper 'off-peak' electricity tariff.
The project will show electricity unit and cost savings by the integration of elevating process temperatures and lowering the refrigerant "delta T" in conjunction with thermal storage.
The new storage system was operational during July and August of 1993, however, the plant did not enter normal service until 1st September, the commencement of the performance evaluation phase.
The storage vessels have been in use every day over the 12 month period from 1st September 1993 to 31st August 1994. It was not until the last 4 month period that the mixing valve arrangements were in circuit and the complete installation fully operational.
The introduction of the thermal storage system to the refrigeration plant has changed the brewery load profile considerably. The electrical maximum demand reduction has improved the site load factor from 42% to 57% and reduced the demand charges significant. This reduction in the site maximum demand has been brought about the transferring of a large portion of the refrigeration compressor operational time to the 'off-peak' night hours.
A summary of the results are as follows :
- 1 MW maximum demand reduction
- 868,000 kWh transferred tothe night period
680,000 kWh reduction in consumption
- 9.6% increase in brewery production during the measurement phase
During the last 12 months there have been process changes which have affected the cooling requirements; faster cooling is now necessary. By taking this into account, and the increased production, the results need correcting as follows :
- 1.2 MW maximum demand reduction
- 950,000 kWh transferred to the night period
- 750,000 kWh reduction in consumption
The maximum demand reduction benefit and the transfer of units to the cheaper 'off-peak' period, are greater than originally expected, however, the reduction in consumption is down. The higher than expected power consumption was due to an accumulation of reasons, namely :
(i) Process changes increasing the overall demand of the refrigeration plant and higher production
(ii) The optimising of the storage to a single temperature system and lower evaporative conditions.
(iii) Extended operation of the compressorsdue to the late introduction of the mixing valve arrangements.
The overall financial benefit of the project is only slightly lower than would be expected. The financial gain from the reduction in the maximum demand has by far the greatest impact on savings. The operation of the system has proved very reliable. The charging of the store is completely automatic with the fully charged point determined by a slight reduction in temperature to -18 deg. C from the normal -16 deg. C reached during the charge period. The only manual intervention is in charging the selection of the compressors required.
For indication purposes, a heat meter was installed in the system. By measuring the secondary refrigerant flow and temperature difference in and out of the storage vessels, the thermal energy removed from the fully charged state is calculated. This meter has not performed well and has given unreliable information to date. The system is presently being investigated.
The project involves the installation of an energy storage system (2x100 m3 storage vessels) using hydrated salts as the phase change medium and storing the energy at -10 deg. C to produce chilled alcohol at -7 deg. C and -3 deg. C.
The method of phase change and the latent heat of fusion to provide high density thermal storage comprises of two storage vessels filled with sperical polyethylene modules. These hermetically sealed nodules contain the hydrated salts.
With the primary refrigerant required to be 11 deg. C below the process temperatures changes have to be made to the brewery profile by elevating the process temperatures by 5 deg. C and reducing the condensing temperatures by 10 deg. C when charging the storage vessels. This gives a benefit of 15 deg. C against a loss of 11 deg. C.
The integration of elevating the process temperatures, reducing the refrigerant temperature differentials and hence saving electricity with the introduction of sub zero energy storage and charging using hydrated salts as the phase change is quite unique and innovatory.
The store will operate as part of the chilled alcohol system and satisfy both the -3 deg. C circuit and -7 deg. C circuit using mixing valve arrangements. The actual number of compressors necessary to aid the cooling demand in conjunction with the store will vary dependent on the daily peak demand. The transferring of a high proportion of the electricity consumption to the cheaper night tariff and the efficiency improvement of the total cooling system will benefit the brewery through annual financial savings of 180,000 ECU's (IRL 140,000).
Programme(s)
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
DUNDALK CO LOUTH
Ireland