The Solution.
We have investigated many options for a solution to the problem:
Accepting that no physical extension to the system could be accommodated and that a 40% reduction in capacity was likewise impossible.
The first area we looked at was designing a ballast, which could work at the temperatures prevailing in the enclosures.
This proved impossible even using " military grade" components, it could not be achieved, the conditions are too hostile.
Secondly we looked at reducing the ambient temperature in the " room" this could be achieved by using large air conditioning units.
This would however only re-create the conditions prevailing in the external system, which is itself unstable.
There were also issues of odour control; noise and energy consumption estimated at approx 30 Kw. per hour.
Similarly when we looked at individual cooling ducts to each enclosure we came across the same problems, plus, any addition of fans or ducts to the top lids of the enclosures would make routine maintenance very difficult. It would have to be disassembled each time access is required.
Neither of the above addresses the problem of the improper positioning of the ballasts and the subsequent electromagnetic interference.
Having established that any type of air-cooling, which vented externally, was not practical we turned our attention to using the effluent as a heat sink.
The effluent maintains a fairly constant temperature our measurements show a maximum fluctuation of 15 to 19 degrees centigrade.
We have designed a modification to the enclosures, which uses a closed loop air circuit to cool the enclosure and which in turn uses a second closed loop in the effluent to dissipate the excess heat.
With this system we can reduce the operating temperature within the enclosure to below the 50 degrees required by both the ballasts and electrical components in the enclosures.
The target temperature is actually 20 degrees above the effluent temperature, i.e. 35 to 39 degrees.
The design criteria for the modification were very strict and included the following.
- Minimal cost.
- No major on site construction.
- No obstruction to normal maintenance.
- No external venting.
- Proper positioning of the ballasts, i.e. 2 inches apart.
- Low maintenance.
- Negligible obstruction to effluent flow or temperature
- Energy efficient.
- Condensation to be avoided.
- A retrofit package not requiring a system shut down.
- The existing management and reporting system not to be affected.
The proposal we are putting forward addresses all of the above.
It comprises a closed loop air circuit in the top of each enclosure, which transfers the heat by means of a heat exchanger to a secondary closed water circuit, which will serve two enclosures.
The primary (air ) circuit.
In each enclosure the ballasts will be repositioned, with the correct spacing onto new baffles.
This together with the alterations to the sub power units will enable all of the components to be cooled in the proper manner.
The revised baffling together with careful engineering of the plenum chamber overcomes possible problems of unequal cooling.
Air will be circulated by two long life fans within the enclosure and through a heat exchanger, which will be maintained at or near the temperature of the effluent.
The heat removed from the ballasts is transferred by the heat exchanger to the secondary (water) circuit.
The temperature gradient across the heat exchanger will be in excess of 20 degrees C.
Access to the lamps and quartz sleeves is maintained.
The present external fans can be abandoned.
The Secondary circuit.
This consists of a small header tank (attached to the side of the top enclosure) a closed circulation pump and stainless steel cooling tubes which will attach to the "legs" of the combined unit at right angles to the flow.
The pump will be of the inductively coupled type without seals.
The coolant will be a refrigerant, to minimise corrosion and microbiological activity.
The circuit will work at low pressure (near atmospheric)
The increase in temperature of the effluent will be so small as to be un-measurable in practical terms.
Performance.
The modification has been designed to maintain the internal air temperature in the enclosure to not more than 20 degrees C above that of the effluent.
We can reduce this still further but it is important to ensure that no possible condensation problems arise.
General.
It is intended that the modification is carried out on site using prefabricated components and will require only the two enclosures being worked on to be shut down.
The external stainless steel tubes will require cleaning at the same intervals as the quartz sleeves and can be cleaned by the same equipment.
The modification will not impede routine maintenance in any way.
The power requirement is very low, the total consumption for all 28 enclosures will be less than 1 Kw.
The present consumption of the external fans is 1.5 Kw. per enclosure.
Conclusion.
We are entirely satisfied that we have correctly identified not only the problem but also the most sensible and practical solution to this problem.
We have reviewed the proposal with the maintenance team.
In order to prove it's effectiveness we need to conduct a field trial.
We would like to carry out the modification to one pair of enclosures (the secondary loop serves two top enclosures.) and to monitor the thermal performance for a period of at least six weeks to ensure that the performance is as predicted.
A successful outcome will be rapidly seen, in that the repeated cycling of the lamps will cease immediately and the inbuilt reporting system will show this.
The cost of this exercise will be £
It must be borne in mind that the development costs already greatly exceeds this figure but these will be amortised over the subsequent production units.
The cost of the production units will be £ per pair of enclosures.
The current cost of maintaining this system as a whole is running well over budget.
In materials alone we estimate it amounts to over £ 28,000 in the year to date.
There is also the labour cost associated with repeated replacements and repairs.
We are not aware of any consequences of "under performance" identified by the environment agency, however the instability of the system will inevitably lead to problems at some point.
Within the next 3 months all of the lamps will require replacement, those that have survived will have reached their rated life, (the UV output falls rapidly after this point) it cannot be either economic nor practical to persist with installing new lamps into an unstable system.
For these reasons this should be treated as a matter of urgency.
Proposed revision to top enclosures. Note spacing of ballasts, access to lamps maintained,
Photograph to illustrate the area where the closed water loop will be situated.
It will be attached to the two side legs at right angles to the effluent flow.
It will be contained within the footprint of the existing frame.
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Commercial Lamp Supplies
Quither Down Business Park
Hayedown
Tavistock
PL19 0NN
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