TABLE OF CONTENTS

In addition heat recovery would need to be incorporated to obtain hot water. The hot
water would be used for:
• Process heating (55°C);
• Floor-/office-/load dock-/ expedition room heating (35°C);
• Bottom floor freezing room heating (12-14°C),
The requirement by the authorities was that the condensing temperature must not
exceed 10°K above wet bulb-temperature
For low temperature side of the processing plant CO 2
applied in cascade with NH 3
,
used on the high temperature side, was selected. CO 2
was used for direct cooling of
the freezers. NH 3
was used only for the high temperature side for cascade purposes, as
the customer’s environmental licence did not allow more than 2000kg NH 3
in the plant.
In addition the plant was equipped with following energy-saving options:
• - Heat recovery-high efficiency electrical motors;
• - Hot gas defrosting: for the freezers the CO 2
hot gas from the plant was used;
• - Frequency controllers;
• - Energy-saving condensers.
The freezing equipment operates following a load programme. In order to achieve the
best COP per type of compressor 1 machine is equipped with a frequency convertor for
speed control at part-load operation.
One of the project bottlenecks was the supply and availability of high-pressure
components, as this plant was one of the first in Europe realised.
The customer is absolutely happy with the installation, which was built in full
compliance with CE-PED.
With regard to future potential savings, as the process needs hot water at temperature
levels of 70 to 80°C there is great interest to adding hot water overcompression heat
pumps operating during the cheaper night-time power price, to buffer hot water for
use during the production process. There is plenty of heat rejected from the high stage
NH 3
cascade plant (over 4 MW per hour during production days), which can be used as
heat source for the heat pumps. Therefore, for future plants where hot water is needed,
the installation of hot water high-pressure compression heat pumps with NH 3
could
help achieve significant energy savings by recuperating the condenser heat from the
cascade NH 3
high stages, which is available in great quantities.
81
Results
A comparison with synthetic refrigerant R507 was considered by Cofely Refrigeration,
who concluded that this solution was much more expensive than the chosen CO 2
/NH 3
concept. After project completion the customer reported that the CO 2
/NH 3
plant is
significantly more efficient than a comparable plant with R507.
In contrast to the original design of 32°C the average condensing temperature on
the NH 3
cascade compressors was reduced to 25°C. This meant a power reduction of
151kWh or 906 MWh based on 6000hrs operation per year (COP-c increase of 8,7%).
This represented an energy saving for the customer of €90,600 (based on €0,10/kWh).
Heat recovery was 690 MW/year (for process use).
The calculated savings amount to 23% on energy, and a 49% saving on CO 2
equivalent
emissions.