Autoclave Water and Energy Recovery at Somerset Hospital
GGHH Agenda Goal: Water, Energy
- Reduce water consumption.
- Reduce energy consumption.
- Reduce expenditure on water and energy.
- Reduction in water consumption – 5000 litres per day
- Domestic hot water generated from waste heat – 6000 litres per day
- Estimated cost saving of R230,000-00 p.a. Pay back in less than 2 years
Autoclaves use potable water to produce steam, and more significantly, to condense the steam in the pressure chamber to draw a high vacuum. During the process this potable water typically runs to waste. This waste water is not only clean but is hot. An autoclave typically uses about 200 litres of water per cycle and this water is discharged at about 40 degrees celcius and runs to waste.
Sustainable Strategy Implemented
Previous strategies focused on the saving water but overlooked the significance of the energy content of the hot water that ran to waste. In view of the water crisis in Cape Town, resulting from several years of low rainfall, it is understandable that water saving received priority.
The current initiative stems from years of experience in reducing energy consumption by using heat pumps. The condenser water from autoclaves is easily recovered by a heat pump. The saving in electrical energy reduces the greenhouse gas emitted by the predominantly coal fired power stations in South Africa. It also reduces the load on South Africa’s aging power stations.
The implementation process involved measurement and analysis of the electrical energy consumed by the autoclaves and then designing a system that would simultaneously cool the waste water for 100% re-cycling and use the energy to heat domestic water to 60 degrees celcius. The design achieved this by:
- Capturing the clean warm waste water in a “Jo-Jo” tank.
- Cooling the water in the “Jo-Jo” tank using a water to water heat pump.
- Pumping the cooled water back to the autoclaves.
- Using the rejected heat to produce domestic hot water at 60 degrees celcius.
On completion of the installation the system was subjected to a full performance test involving metering and recording of water flows and electricity consumption. From the water and energy measurements the Coefficient of Performance (COP) of the domestic water heating and of the overall system was calculated.
The installation has water meters and temperature indication installed so that the maintenance personnel can monitor the performance.
- The saving in water varied from 4500 litres per day to 6000 litres per day. An average saving of 5000 litres per day is anticipated.
- The domestic hot water generation varied from 6000 to 7000 litres per day. An average generation of 6000 litres per day is anticipated.
- The COP of the 60 degrees celcius hot water generation was calculated to be 3.3 and the overall COP was 5.6 (over a 24 hour test period).
- The cost saving in respect of water is expected to be R50,000 p.a. and electricity R180,000 p.a.
- The pay-back on investment will be less than 2 years.
The roll-out to other hospitals is already in progress.
Somerset Hospital is a 340 bed Regional Hospital providing general specialist services. It is a referral hospital for an estimated 500,000 people who are reliant on public health services.
Main Article Image of Somerset Hospital from Wikimedia Commons
Information and Images courtesy of Western Cape Department of Health