Energy Saving in Tower Building

 

Energy Conservation Opportunities

in

Water Supply System

of

Multi Storey Buildings

 

As general practice all multi storey buildings have water tank on the terrace. All occupants get their water supply from this tank. Obviously tank size has to be big enough to store sufficient water required for all occupants. Pump-set is provided for pumping water to the tank either from bore well or sump. There is distribution piping network for all apartments at various floors.

While examining various alternatives, it is found that there is huge scope for energy saving. This requires radical changes starting from design of the building.

Masonry

Water storage tank is to be build for each floor instead of common tank at terrace. These tanks may be like column of tanks one over the other. Tank height may be equal to floor height and base as per water storage requirement for one floor only. There will be no tank on ground floor level. Top tank will be on terrace. This means numbers of tanks are as per numbers of the floors in the building. Column of tanks may be adjacent to common passage for easy access. Useful height for water storage of tanks will be equal to floor height minus manhole on one side, preferably towards passage.

Plumbing

All occupants on any floor will get water from the tank just above their floor. Means all occupants of forth floor will get water from the tank at fifth floor level. Water supply distribution piping network will be accordingly floor wise. Common feed line will run from water pump up to top tank in terrace. There will be tapping from this mail line to each tank at respective level. Float valve (Ball Cock) is provided at inlet of each tank except at top. Alternatively solenoid valve operated by float switch can be used in place of float valve.

Electrical

Water pump motor operation is regulated by its control kiosk. Control box will have level control system in addition to all relevant preventive elements like starter with overload and no volt protections. Only top tank at terrace has maximum level sensor to stop the pump. Minimum level sensors are installed in all other tanks at each floor to start the pump. Minimum level sensors in all the tanks will be parallel so that pump is started due to low water level in any tank.























Operation

The operation of the scheme is simple. On start of the pump the water rise up in the feed line. In the beginning water will divert through lower most tap line and fill the tank. Float valve will stop inflow when tank is full. Now water will rise further in the main feed line. Now water will divert through next tap line and fill the tank. This will continue till all the tanks get full. Maximum level sensor in top tank at terrace will initiate motor stop signal when it is also full. Ultimately all the tanks will be full when motor stopped by sensor in top tank.

Water level in various tanks falls according to consumption by occupants in respective floor. Pump is started when level fall below the minimum level in any tank. As discussed earlier, all the tanks are top up starting from lower tank to top tank irrespective of starting signal from any tank. Motor stops only after top tank is full. So all the tanks will be full when pump stops. Hence no frequent start stops operation of the pump.

Energy Saving

In existing common single tank system, water requirement of all occupants of all floors has to pump up to the top tank in terrace. Whereas water has to be pump only up to the required level for occupants at respective floors in the proposed setup. So energy wasted in undue pumping of water up to higher level is avoided.

Calculations indicate that energy saving by this arrangement is about 20% in three floor building and about 30% in five floor building. Maximum energy saving may be up to 50% in building of more floors.

Cost Comparison

Cost of proposed scheme will not be higher compared to tradition scheme. Tradition scheme requires single tank but has to be very big and sufficient strong for huge quantity of water. Also all materials including curing water and workers have to be taken up to the terrace. This is addition cost of shifting as above and time spent in shifting to terrace. Proposed scheme requires multiple tanks but all simple small tanks at lower heights.

 Additional Advantage.

In addition to saving of energy as above, this has following advantages.

  1. Tower buildings behaving like inverted pendulum. Center of gravity of the building will be higher in traditional scheme compared proposed scheme. This is important advantage from point of view of stability of building. Also sloshing effect of huge water storage at very height aggravates seismic danger. Both above are very important from point view of the safety of building during quake. This is minimized in proposed scheme.
  1. Occasionally observed in traditional schemes that upper floor occupants may not get water during peak hours particularly in the morning when more occupants start drawing water at the same time. Of course this problem can be reduced to some extent by graded down line. However it is not perfect solution. But proposed scheme has no scope of such problem.
  1. Water pressure may be normal at upper floors but it is excessive at lower floors. Extreme high pressure cause leakage/passing through joints and stop cocks. This is dual loss due to wastage of water and energy spent for pumping.
  1. Water pressure is excessive at ground floor. So water is rushing at very high force. Ultimately it bounces back and over flow off the bucket. Huge water is wasted in this way. Again this is dual loss due to wastage of water and energy spent for pumping.
  1. Very rare but extreme case can be about careless and mischievous member in the building. Someone may not care to stop leakage or properly closing the cock or forget to close the cock and went out. Some mischievous intentionally let water directly to drainage. All the occupants in the building face loss of water in such event. Also it is rather difficult to pin point the culprit amongst numbers of occupants at different floors. But similar problem remain confined to concern floor only and easy to identify the one amongst limited occupants on floor in proposed system.

Scope                               

Land cost in urban area is very high. All new residential or commercial expansions are multi storey. So there is big scope for energy saving, water saving and reducing risk to citizens due to instability.

Conclusion

Some floor space is engaged for construction of floor wise tanks. Normal water tank height is 4 to 5 feet. Height available in floor wise tank is floor height minus half meter left as manhole. So floor space require is less with more available height. Calculation indicates that floor space required for tank column is less than one percent of total floor area.

In view of the above, modified water supply system should be adopted primarily for energy saving with added operating advantages as above.

Proposed scheme has three virtues

  1. Enhance Seismic Security

  2. Energy Saving

  3. Water Saving.

Recommendation

In view of the above, government should encourage this scheme by appropriate directive to concern such as….

  1. Bauro of Energy Efficiency can include this in building code.

  2. Floor space of tank column can be exempted from criteria of FSI, approval fees, property tax, etc by local authority.

  3. This may be in syllabus of civil engineering.

  4. Central/State government can offer incentive in the form of subsidy.