Bringing old chillers up to new standards
Refurbishing old chillers brings many of the benefits of replacing them — but at much less cost and with much less disruption. Trevor Dann explains.
In the current economic environment the pressure is on to save money now by reducing capital spends and to continue to save money later by reducing running costs, particularly energy usage. However, the first requirement often over-rides the second, as reducing running costs often requires huge capital investment to benefit from modern technology.
This principle applies to water chillers as much as any other complex equipment, but as many larger buildings will see over half their energy bills assigned to chillers, any percentage saving on power will have a big impact.
As a rule of thumb a reasonable-quality medium-size water chiller with a cooling capacity from 200 to 800 kW can often be priced as follows.
100 x nominal cooling (kW) + 25% (in £s)
However, there are many other costs associated with replacing an existing chiller. They include craneage, disturbance of services, installation fees, commissioning, design consultants etc. They can be taken into account by doubling the approximation above and trebling it to replace a chiller that has been built in
Installing a mid-range 500 kW chiller will therefore cost about £60 000 (500 x 100 +25%= 62 500) plus a further £60 000 to remove an existing chiller — giving a total project cost of about £120 000.
For that £120 000, we will remove a substantial, and mostly intact defunct, and presumably life-expired chiller. Although much of the scrap will be recyclable, the scrap value will be negligible and normally lost in the overall project cost.
The new chiller will almost certainly be imported — over 90% are. Even if the new chiller is assembled in the EU, a good proportion of the base assemblies will emanate from beyond the EU, which is disadvantageous to our balance of trade.
Finally every last nut, bolt and widget of the new chiller must, by definition, be ‘new’. Each requires smelting, moulding and casting, and each base resource requires some degree of mining from raw ore.
So the environmental and trade hit of a complete new chiller is high.
So back to the beginning of this article …
Energy efficiency and reliability, along with environmental factors such as phasing out R22 phase out, are key drivers for procuring a decent new chiller. However, considering that some two-thirds of the weight of the chiller being replaced is simply a large metal box and frame, often in reasonable condition and pretty much duplicated by the new chiller, why not look again at the potential economics of refurbishment?
The 95%+ proportion of chillers installed use vapour compression as the primary means of cooling means, and their main components are as follows.
1. Chassis/frame
2. Compressor(s)
3. Condenser(s) with fans for heat rejection
4. Evaporator
5. Pipework system
6. Electrical and controls system
The most common problems with old chillers affect compressor(s), heat rejection and the electrical and controls systems. The evaporator may sometimes be a concern. So let us now focus on the main problem areas.
Compressors have dramatically improved in terms of both reliability and efficiency. For smaller systems, the scroll compressor is an efficient, and almost throw-away component. For larger displacement systems above 200 kW sub-system capacity, the screw compressor is now firmly established as the most widely applied, reliable and energy- efficient method of vapour compression.
Condensers operate in mostly hostile weathered environments; being made of friable mixed metals such as copper and aluminium, they are prone to significant deterioration after several years’ service.
Chillers from the late 1980s and early 1990s would be expected to last 15 to 20 years. However cost pressure over the past decade or so has seen an alarming increase in the use of ‘value’ equipment, where much emphasis has been placed on using the bare minimum of expensive aluminium and copper. The result is that many chillers bought on price will suffer condenser failure after just a few years’ service (with what environmental impact?), but for most air-cooled projects replacing the condensers is a key and almost routine expectation of an upgrade.
Electrical and controls systems are an area where age degeneration will be a crucial factor in determining life expectancy. However, modern controls and a new compressor can have a significant impact on residual life and the efficiency of an upgrade project. Modern electronic controls and modern screw compressors can reduce energy consumption substantially; 60% is our highest achievement, although 30% is more typical.
All these benefits of refurbishing a chiller cost much less than replacing it with a new chiller, and the extent of refurbishment can be tailored to the requirements of each project. As the table shows, refurbishing a 500 kW chiller is about half the cost of replacing it. The life expectancy of such a refurbishment is at least 10 years, and the energy efficiency is the same as a new chiller. If the work is carried out by ThermOzone as a Re-Chill upgrade, a warranty of two years or longer is offered.
In our experience, chiller refurbishment needs to take due account of the site client’s knowledge and requirements. We listen to the woes of the client and his original chillers, and also his specific needs, and tailor a solution that addresses these concerns, and will take due account of any fundamental limitations.
Before embarking on such a refurbishment, it is important to properly educate site clients what to expect in terms of project implementation and onward effect. It is also important to inspire confidence into those who have to make the often considerable leap of faith that can be needed to take the decision to upgrade a chiller.
Trevor Dann is operations director with ThermOzone Ltd
