The Elephant Exhibit - Chester Zoo

The Elephant Exhibit at Chester Zoo is served by a single air handling unit (AHU), the duty of which is to provide mechanical air handling for the exhibit. The in-house Maintenance Team identified opportunities for energy saving by the application of ‘demand matching’ principles and technologies primarily control optimisation and a variable speed drive. An energy efficiency project was undertaken during the period July – November 2008 with regards to the AHU and associated controls.


The programme of works delivered a wholly ‘demand matched control strategy’ for all AHU functions, i.e. heating, cooling and ventilation. Prior to the upgrade, the exhibit AHU electric motor ran at 50 Hz and used 34.5 Kw/hr / 24hr/7day, 100% load. Subsequent to the works the AHU motor runs at 38 Hz rather than 50 Hz. Electric motor power consumption has dropped from 34.7 Kw to 15.1 Kw.


This evaluation was undertaken using electricity meter ‘E33’ which is exclusive to the AHU. The meter readings have been validated using a digital energy data logger and the variable speed drive user interface. For meter readings see pages 4 and 5 of this report.


The variable speed drives were fitted 7 Aug 2008 and smart controller and demand matched ventilation fully integrated in November 2008.


Benchmark environmental data was taken prior to the works and values have not been compromised by the changes.





January to July: i.e. the period prior to the upgrade works total consumption 140529 Kw hrs:

Monthly average consumption 20075 Kw hrs


August to December: the period subsequent to the works total consumption 32310 Kw hrs:

Monthly average consumption 6462 Kw hrs.


It is apparent that subsequent to the project works, a reduction of 67% was achieved in average monthly consumption for the last five months of 2008. It should be emphasized that as the AHU motor previously ran continuously, this is a real saving and does not relate to seasonal variation. 68065Kw/hrs saved to end 2008




In the five months evaluated to date in 2009, January to May, average consumption in comparison to the equivalent period in 2008 has fallen by 74%. The lowest fall was in January at 52% and the highest in May at 93%. Estimated 74786 Kw/hrs saved to date in 2009.

See 2008/09 comparison table page 2 of this report


Projected annual Kw/hrs saving = 178266

Projected annual £ saving @ .11 pence per Kw/hr = £19609

Projected annual Carbon saving @ .43 kg carbon per Kw/hr = 76654kg



eturn on Investment

The contractor’s costs amounted to £8500, Planning and Management of the project and Site Technicians time and enabling works amounted to approximately £1000. Total project cost £9500. Estimated monthly saving is £1634 (@ 11pence Kw/hr) therefore payback is less than six months.


In addition the service life of the air filters used on the AHU has increased by around 60%. An unforeseen benefit was noise reduction on the occasion of the AHU fan having to be stopped, such as for maintenance as now it has a ramped shutdown.


Savings on gas usage will also be likely as a result of the works undertaken.  These will be evaluated at a later date.




Savings in regards to the installation of Variable Speed Drives have been consistent with that expected, when applying cube law to motor speed/energy consumption i.e. typically energy savings in excess of 50% for a 20% speed reduction. This is evident when looking at the January comparisons for 2008 and 2009 which show a 52% energy saving.  In January as heating requirement is high, savings from the demand matched ventilation strategy is minimal. The 52% represents a baseline saving, most directly attributable to the variable speed drives and secondly, to controls optimisation eliminating heat/cool cycling.


Savings from the demand matched ventilation strategy are most evident when looking at the May comparisons for 2008 and 2009, which show a saving of 93%.  This is as result of advantageous ambient temperatures which heated the building to the required degree and advantageous passive ventilation. If the air quality parameters are met in this situation, the AHU is ‘OFF’ so effectively saving 100% in comparison to the original control scheme.



Kw/hr Consumption: Comparisons 2008/2009 (Meter reference E33 Elephant Exhibit AHU)









Kw hrs usage


Kw hrs usage


2008 > 2009

% Variation



£ Saving @

 11p Kw/hr




- 52





- 65





- 76





- 87





- 93












































Elephant Exhibit; Description of works


The ‘demand matched control strategy’ for control of heating, cooling and ventilation was achieved using a Building Management System to deliver controls optimisation, and by means of an external ambient air temperature sensor and internal temperature sensors. A system dead-band was established to prohibit a heat/cool cycle being apparent on scrutinising the system.


Appling a demand matched ventilation strategy has proved particularly beneficial as the exhibit characteristics promote ‘advantageous air’ i.e. plentiful fresh air infiltration and a considerable number of building openings.  This means that for substantial periods, the building AHU is now in a ‘no demand mode’.  Acceptable air quality parameters were established using CIBSE codes and by air quality comparisons in other exhibits.


In addition to the controls optimisation, a variable speed drive (VSD) has been installed which has enabled demand matching control of the AHU electric motor.


Controls Equipment Used


1 – Trend IQ3 controller

1 – IQ view Mono Fascia display unit

1 – TB/TO Outside temperature sensor

1 – TB/TI Duct temperature sensors

1 – Air Quality Sensor

2 – HT/ST Room temperature & humidity sensors

1 – 37.0Kw Danfoss inverter speed drive