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Post by CSLR on Jul 24, 2006 17:54:56 GMT
We started to digress (as usual) on a couple of other threads, but the subject was so interesting that instead of straying off-topic, I thought that it might be worth starting a new thread.
The subject is, the ever increasing heat Underground and the measures that are/could be taken to combat it. It has been made clear that this is influencing future train design, it is already being addressed experimentally at stations and Uncle Ken has made it clear that it is an issue that he wants tackled.
As I understand it, (info confirmed by prjb) there is an experimental scheme at Victoria which pumps rising ground water through a type of heat-exchanger. The water absorbs the heat from the air and in return, the surrounding air is lowered by around three degrees.
I have an interest in combining existing technologies in a way that can increase the efficiency of both (or more) technologies. Some people do not like this type of idea but, by utilising an element that would be wasted by one technology and passing it on to another one that is seeking such an effect, the efficiency of both can be dramatically improved.
It seems to me that what we have here is surplus heat; meanwhile, we are exploring new energy efficient ways of creating heat. One of these is geothermal energy. Before we discard this as a pie-in-the-sky scheme, it might be worth noting that Elton John, Richard Branson and the Queen all use it. The idea is that a series of pipes are buried underground, water is pumped through them which increases its temperature slightly (3 degrees is just about right). By passing the slightly warmer water through a heat pump, hot water is created (the best way to describe it is that it is the reverse of how a refrigerator operates).
This system works well if you have a big garden (eg. the back yard at Buck Palace) but in a city, it involves expensive boreholes. So, what about connecting the surface offices up to the tube?
The tube system gets cooled down and LU can generate some income by selling cheap heating and hot water, or using it in its offices (places like Stockwell, seem ideally suited).
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Post by stanmorek on Jul 24, 2006 23:10:04 GMT
Alright then I think I follow you but am still not clear how the two techniques are combined. A heat pump takes heat from the underground network and concentrates it to heat up water which is then pumped to the surface but where does geothermal energy come into it? My understanding is that cool water is pumped down to hot rocks and pumped back to the surface as hot water/steam. Granted the water going down could help cool the tube but first we need hot rocks which are also within reachable distance of where we want the cooling effect to take place. The deeper we need to bore the higher head of water that needs to be pumped. This would require more energy to power the pumping system and the pumps themselves would generate heat. Sorry but I may have misunderstood the finer points of your proposal!
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Post by Deleted on Jul 24, 2006 23:30:49 GMT
I'm still not really that bothered about heat on the tube. At the moment, any measures they do take, aren't really worth the money, IMO. We have what, 8 weeks worth of hot weather a year, if that!? I can't justify spending millions of pounds on it!  The cooling system they are currently trialing sounds like a very good idea though, and would love to know if anyone has experienced it working!? However, are these pipes like normal pipes, and in winter, when its can reach sub-zero, would they be prone to freezing? |
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Post by CSLR on Jul 25, 2006 2:44:13 GMT
Alright then I think I follow you but am still not clear how the two techniques are combined. A heat pump takes heat from the underground network and concentrates it to heat up water which is then pumped to the surface but where does geothermal energy come into it? My understanding is that cool water is pumped down to hot rocks and pumped back to the surface as hot water/steam. Granted the water going down could help cool the tube but first we need hot rocks which are also within reachable distance of where we want the cooling effect to take place. The deeper we need to bore the higher head of water that needs to be pumped. This would require more energy to power the pumping system and the pumps themselves would generate heat. Sorry but I may have misunderstood the finer points of your proposal! This system does not rely on hot rocks and a pump, neither does it deliver hot water or steam to the surface. What you are referring to is an early type of geothermal system that operates on a different principle. The system that I am discussing is already employed in the Queen's Art Gallery in London and is currently being planned for the whole of Buckingham Palace using heat collected from beneath the pond in the back garden. Several other versions are already in use throughout the UK - so we know that it works. This system does not require water to be heated to its final temperature in one stage. It simply requires an increase in temperature of around 3-4 degrees. Because this is exactly the temperature difference that has been mentioned in relation to the Victoria experiment, I am beginning to wonder if those carrying out the tests are actually planning to use this very system - if not, I expect that someone will now prompt them to the possibilities. There would be no heat added underground by the heat pump (or any other pumps) these are all on the surface, just as they are in the systems that are already in operation elsewhere in the country. For the purpose of my original post, I did not explain the full details, which has led to misunderstanding. What I described as a 'heat pump' is actually a combination of various parts, all of which are on the surface. The incoming water (from LU) would pass through a sealed evaporator and into a compressor (that is what you hear turning on and off on the back of a refrigerator). The compressor increases the pressure of the fluid causing the temperature to rise to around 95 degrees F ! (that is not a typing error, that is fact and it is similar to the heat that you are constantly trying to lose from the back of your fridge). The high pressure hot water passes into a condenser which transfers the heat for use in a heating/hot water system before returning to the evaporator through an expansion valve where the pressure and temperature will drop again. Remember, this is a system that is already proven and which is marketed commercially by several companies. It is quite difficult to explain in words, so I will see if I can find an illustration that explains it more clearly, and will post it later today. One question that might be asked is could it be made commercially viable? Consider that a borehole for such a system will cost tens of thousands of pounds (rising to hundreds of thousands in some cases) and you will see that running pipes into the tube would be a viable (marketable) alternative. You are correct in your assumption that the pumps and heat transfer system use energy, but this is considerably less than would be used in a conventional heating system. As a rough guide, four units of energy are gained for every unit of energy used. The remaining 75% of energy is gained from the heat that has naturally transfered into the water through the underground pipes. As a bonus, it is possible to use that cooling effect created by the heat transfer to cool the deep-level tube tunnels/stations instead of wasting it. Or if you look at it the other way round, you use the method to cool the Underground and then use the surplus heat on the surface - it is the same difference. To summarise. 1. You do not need hot rocks. 2. You do not need differences in temperature any greater than is being achieved by the current experiment at Victoria station. 3. All pumps are on the surface, so no heat is being added underground. 4. It could be made commercially viable as a saleable commodity. |
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Post by CSLR on Jul 25, 2006 3:04:11 GMT
I'm still not really that bothered about heat on the tube. Other people within LU are apparently taking the matter very seriously - thus the post. At the moment, any measures they do take, aren't really worth the money, IMO. We have what, 8 weeks worth of hot weather a year, if that!? I can't justify spending millions of pounds on it! Exactly. That is why I am suggesting that they look at a system that makes use of the waste heat and is commercially exploitable. Remember also that we are not just talking about an 8 week period. The underlying problem is the uncontrolled rise in background temperature on the deep-level tube system. The cooling system they are currently trialing sounds like a very good idea though, and would love to know if anyone has experienced it working!? It sounds like it does work well, but it could be costing unrecoverable amounts of money, which is something that what we both agree should be avoided if possible. However, are these pipes like normal pipes, and in winter, when its can reach sub-zero, would they be prone to freezing? The system is a sealed unit and the water is a brine that prevents it from freezing. As I understand it, the Victoria system uses ground water and there is no brine in it. |
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Post by Deleted on Jul 25, 2006 8:01:32 GMT
I like your idea CSLR. It certainly makes a lot more sense than all the others I've heard! And what makes even more sense, is that the money raised from this, could be put into ways to cool the tube for those 8 weeks or so, instead of using money thats coming from the improvements bank!
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Post by Hutch on Jul 25, 2006 8:13:05 GMT
I first heard of heat pump technology from my chemistry teacher in the mid 1970’s. He was proposing to heat his house using heat from his back garden – a bit like the Buckingham Palace scheme but on a slightly smaller scale! Rather than trying to imagine things in reverse, think of a normal refrigerator which pumps heat out the back when running – stick your hand over the back and you will feel the heat – if you can reach the radiator system on the back (many are now hidden) you will feel that it is very hot. With the domestic heat pump you simply put the cooing part of the fridge (expanded many times) under the back lawn. You hopefully never manage to freeze the lawn as the heat is constantly replenished by the outside environment – rather like keeping the fridge door open constantly! The challenge with CSLR’s ( greetings again!) idea is getting the heat out of the air (low thermal conductivity) rather than the ground (high thermal conductivity). To compensate for the low thermal conductivity of air you would need to have the heat exchanging elements locally cool the air down much lower than 3º and then force lots of air past it to create an effective exchange of heat. But then you would have something that we are all familiar with – it’s called an air conditioner. ;D |
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Post by CSLR on Jul 25, 2006 8:35:55 GMT
The challenge with CSLR’s ( greetings again!) idea is getting the heat out of the air (low thermal conductivity) rather than the ground (high thermal conductivity). To compensate for the low thermal conductivity of air you would need to have the heat exchanging elements locally cool the air down much lower than 3º and then force lots of air past it to create an effective exchange of heat. But then you would have something that we are all familiar with – it’s called an air conditioner. ;D There are actually several ways that this could be done. One way would be to run finned pipes along the roof of a tube station - you could certainly get a lot of pipe up there and, with a little creativity, you could make it look like part of the decoration. Air flow would be aided by the movement of trains, but do not forget, hot air rises, so you also have natural circulation as the warm air goes up to the pipes and the released cool air comes down. One other place that might be considered is ventilation shafts. These already have the facility to move large amounts of warm air in an upward direction. Although these seem like logical locations to use, they are not always near to property that could use the reclaimed heat. Although there is the advantage that any installation would be unobtrusive, there is the problem of moving the cooled air in the right direction, which would mean a re-think of the overall design of the ventilation shaft. |
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Post by donnytom on Jul 25, 2006 10:44:17 GMT
The Brussels underground had an effective way of cooling us while moving- many vents scooping air into the carriage from the roof of the train. Quite a simple solution, but only useful when the train's moving, and if the outside air is cool.
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Post by CSLR on Jul 25, 2006 11:45:27 GMT
The Brussels underground had an effective way of cooling us while moving- many vents scooping air into the carriage from the roof of the train. Quite a simple solution, but only useful when the train's moving, and if the outside air is cool. I mentioned this method in another thread a few days ago when referring to Standard (pre-38) tube stock. They had exactly the same device and it worked very well indeed. In fact it worked so well that the obvious happened - we stopped using it and are now scratching our heads trying to work out how to achieve the same results with more complex designs and equipment. You know the rules: 'If it ain't broke, keep altering it until it is. If it still won't break, scrap it.' Two things about this design:- 1. Moving air always feels cooler than static air. So the air movement that these scoops create (without any assistance from a power operated fan) is really useful. 2. On the Standard tube stock, the scoops were close to the tunnel roof and caught any air movement, even if it was caused by another train during a delay. Because most modern-day designers will never have experienced some of the refinements that have subsequently been abandoned, I suggested that someone borrows a Standard stock car from Acton, fills it with designers and takes it for a trip through a tunnel. If this idea is to difficult to arrange, they could always prove the point with CAD without even leaving their desks. In doing so, they will probably justify their hard work by showing that air movement could be improved marginally by varying the angle of the scoop by 0.0001 of a degree: but I would be willing to bet that those designers working at their drawing boards in the 1920s and 1930s got it pretty damn close. |
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Post by CSLR on Jul 25, 2006 14:44:48 GMT
Here is an animated illustration that I found of the cooling/heating system. This particular site is intended for domestic users using a borehole or pipes buried in trenches, so not everything in the accompanying text is relevant. It will, however, show you exactly how and why the system works. You will note that air is clearly mentioned on the diagram as one of the three useable sources that heat can be extracted from, although it is not illustrated further. www.earthenergy.co.uk/how_it_works.php |
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Post by Deleted on Jul 26, 2006 10:23:47 GMT
As I said in another thread, basic Physics says that a moving body has a certain amount of kinetic energy, which is converted into heat in bringing it to a stop. It does not matter whether the braking is rheostatic or friction: it's the same amount of heat. That is why the tubes have been getting hotter since they were built. The temperature was starting to be a concern 50 years ago, when all the trains had friction brakes.
And, while I am at it, it's not the cast iron tunnel linings that are absorbing the heat: it's the clay on the far side of the cast iron.
{Edit: typo}
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Post by orienteer on Jul 27, 2006 18:28:58 GMT
On the other hand, regenerative braking produces electricity rather than heat.
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Post by Deleted on Jul 27, 2006 22:36:58 GMT
Agreed. Regenerative braking (when it works) converts the train's kinetic energy into electricity which is then used by another train. This reduces the total amount of electricity used. And as all the electricity used by LU is eventually converted into heat, regenerative braking will somewhat reduce the amount of heat pumped into the tunnels.
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Post by yellowsignal on Aug 22, 2006 21:22:54 GMT
Heat- and cold storage is dependant on the type of soil, it uses two aquifers (underground "bubbles" of groundwater).
Usually the two aquifers are about 100-150 metres apart and 50-100 metres below ground.
A compressor isnt needed, the system uses a heatexchanger which needs a few degrees of difference in temperature.
In the summer water is pumped up from the "cold" aquifer the heat is taken from the air and pumped into the "warm" aquifer. During winter heat is pulled out of the warm aquifer, energy is released into the building via the heatexchanger and the water is pumped into the cold aquifer.
In the case of LU the heat could be delivered during winter to officebuildings in the vicinity of the station or equipment location or just dissipated into the air.
This system is economically viable for a cooling capacity of 250-300 kW or a building of 6000 m2 or bigger.
The equipment room is about 25%-40% smaller compared to conventional airconditioning plant. It uses 80% less electricity for cooling.
Brine isnt needed since the entire system has a watertemperature of about 10-15 degrees with no stagnant water.
On LU properties the biggest problem is space i think, you still need a considerable plant room and space is at a premium at most stations i think. What could be done is a central plantroom serving two or more stations where a building outside the stations is used for the equipment. The heatexchangers/cooling elements would need to be installed in the stations because of space restraints. The dust in the tunnels could be reducing efficiency.
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Post by Deleted on Aug 22, 2006 21:36:04 GMT
On LU properties the biggest problem is space i think, you still need a considerable plant room and space is at a premium at most stations i think. Although I do agree with you, there is probably quite a bit of unused space at some stations. For example in the circulation areas between platforms, there is often quite a bit of unused space above peoples heads. There may also be disused lift shafts, corridors, and other unused spaces at some stations. |
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Post by yellowsignal on Aug 26, 2006 19:02:54 GMT
You''l need more than that, and you need to lift in some heavy pieces of equipment.
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Post by woody on Aug 27, 2006 7:50:48 GMT
and you need to lift in some heavy pieces of equipment. Ahh - a link to escalator safety  So the heavy equipment will have to be made in very little pieces and assembled underground unless................. Why don't we use the trains to take maintenance equipment to platform level?  Or has that been rejected more than once in the past? |
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Post by yellowsignal on Aug 27, 2006 12:39:24 GMT
It would be cumbersome to have to move it in by train. Plus you have to put in some pipes carrying water, it's safer to have that stuff somewhere else in case a pipe starts to leak.
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Or has that been rejected more than once in the past?
