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Dialysis water cooler
- 1 Background
- 2 Project details
- 3 Online cooling
- 4 Other potential solutions
- 5 Future work
- 6 References
- 7 Contact details
Dialysis in the desert
In remote Australian communities, Aboriginal Australians suffer kidney failure at a rate that approaches 10 times the national average. Transplants are rare and frequent dialysis is usually prescribed. Many dialysis patients are elderly and senior members of these remote communities. In an effort to improve the social health of both communities and patients, there has been a recent push to increase dialysis services within remote communities and clinics (Devitt and McMasters, 1998, pg.67). Unfortunately, many of these communities are in arid regions, which means town water tends to be warm where it comes out of the tap.
Remote water temperature
In remote communities, town water is typically raised from the aquifer, then treated and stored in large tanks, often on the top of a hill in the sun. Tank water is piped over-land to various points including each remote clinic, where it may be stored in a smaller clinic’s tank. In summer, air temperatures may approach 50C. By the time the water gets to a clinic it is usually quite warm. Dialysis water pre-treatment depends on small RO systems, which tend to lose effectiveness as the water temperature rises, eventually posting errors and shutting down with water temps around 35C.
The RO systems are designed to fail safely when the incoming water temperature is too high. However, any equipment failure may cause dialysis treatments to be cancelled. Since patients need dialysis treatments on alternating days, a delay of more than one day means transport of the patient to a regional centre (usually Alice Springs) for treatment. This is both expensive and detrimental to the health and wellbeing of the patients. In short, the consequences of missed dialysis are significant from a patient wellbeing and public-health perspective.
To provide a source of cool water (below 35 C) to remote clinics at a rate of 1L/min per dialysis machine.
A remote community water supply may reach temperatures greater than 45 C. An RO machine will alarm when its supply temperature is greater than 37 C. An effective pre-cooling device would be one that could reliably take 10-15 degrees C off the supply water temperature at a rate of about 1 L/min. This is equivalent to about 1.2 kW of heat that needs to be extracted from the incoming water.
One of the main challenges of this project involves finding a suitable place and means to sink the heat that is extracted from the water. It is difficult to sink the heat into the outside air, as it can be much hotter than the supply water. Such techniques have been attempted by using chiller packages that operate outside a dialysis clinic and attempt to pump heat from the water directly into the even hotter air. This has been shown to be unreliable due to solar loading and other challenges of heat transfer.
Air conditioning cooling capacity
One approach is to sink the heat into the room's inside air and allow the air-conditioning systems to pump the heat outside. The main advantage of this approach is that the air represents a thermal store that can quickly absorb the heat from the water before it is slowly pumped out by its air-conditioners. The second advantage is that there are usually more than one split-system air-conditioning unit installed in each clinic, providing ample capacity to pump heat from the inside air to the outside environment. A typical split-system air-conditioner has a cooling capacity of about 8 kW. This is more than six times what is required to pump out the heat required to run a single dialysis chair on a hot day.
Various informal methods have been attempted, such as running hose through a chest-freezer, draping tanks with wet cloth, storing water in a tank inside the clinic. None of these solutions have been engineered - they are mostly guesswork. At present, sites have purchased chiller packages - these are worth $8-10K each, are heavy, are not that effective at higher temperatures and are prone to failure.
- A good solution to this problem would be inexpensive, lightweight, effective, reliable and robust for us in remote sites.
- As maintenance is difficult at a remote site, a good design would be reliable and low-maintenance and/or usermaintainable
- Another approach to maintenance is to make the device lightweight and portable, such that it could easily be loaded by a single person into the cabin or tray of a 4WD and installed with a minimum of technical expertise.
- A good design would be able to be used together with any other cooling system without having to reconfigure the plumbing of the equipment or building.
Other potential solutions
Some stakeholders have suggested pre-cooling an indoor tank full of water for dialysis, to save cooling it on-demand. This may be done to take advantage of the cooler night-time weather for cooling water, then storing it until the morning for treatments. By using a heat-exchanger similar to that described for the online approach, water could be circulated through a storage tank and a heat exchanger device over a 12 hour period and the heat could be dumped into the building's inside air and allowing the air-conditioner to pump it outside.
What shape and size of water storage vessel in an airconditioned room can chill 300 L of water by 10 C in 12 hours overnight?
The main design challenges with this approach are as follows:
- A large tank needs to be constructed and installed within the building.
- The entire volume of the tank needs to be cooled for any of it to be usable.
Water used at 1.0 L/min for five hours is 300 L. Rather than have one tank per chair, it makes sense to cool all the required water for all dialysis chairs. To run two chairs requires 600 L of water for treatment, plus extra water for cleaning cycles before and after each treatment. If we aim for a minimum of 1000 L tank capacity for two chairs (2000 L capacity for a four-chair clinic), then we must sink a large amount of heat overnight.
With a heat exchanger operating at twice the capacity of our tested online prototype, it is possible to cool sufficient water and store it in a tank overnight. Generally speaking, it would appear that the optimal combination is a small tank and a large, efficient heat exchanger.
What is the optimal capacity of offline storage volume and heat transfer capacity (kW) to provide enough cooled water in 12 hours overnight for two dialysis treatment chairs?
For mobile dialysis, the air-conditioning units are small and cannot be expected to handle the extra load of water cooling. Some stakeholders have suggested Peltier modules or similar electronic heat-pump may be developed for this purpose. One mobile unit has a "dispatch hatch" with dimensions 1200 mm side and 500 mm high with a door that hinges upward, which may be used to pump heat from inside a mobile dialysis clinic truck-body.
What is the simplest active heat-pump that can be built to transfer heat from water to air at 1.2 kW per dialysis machine, through a small opening in a vehicle?
Heat collection using phase-change material
There has been recent research in both the medical-device field  and in building-temperature management  regarding the use of phase-change material or salts as a combination of temperature-control and energy-storage. This type of project is probably the right kind of size and scale for this kind of application.
What type and quantity of PCM is needed to extract and store at least six kWh of heat from a potable water supply delivered at 1.0 L/min?
Appropriately sized packs of PCM could be exchanged and cooled offline or offsite.
Where else in the world would this be useful, and who else has solved this problem and in what ways? Is this technology useful in other parts of the world? This problem exists in about 10-20 remote communities in Central Australia, and there are rumours of a similar problem in South Australia. There may be similar problems in arid/hot regions of other countries that suffer chronic kidney failure (Sahara desert, perhaps?). There is more to be said about this later.