Remedies To Increasing Water Demand In Commercial Buildings
Any commercial building is going to have air conditioning system to provide comfortable atmosphere to its occupants. The first step an MEP Engineer should do is to reduce the heat load. It will directly reduce electrical power consumption and water demand...
The need to conserve water, its high scarcity and undependable supply in many parts of the country has made MEP design engineers study each new building project carefully to evaluate the possibility of maximum water savings. All the Municipality norms, Eco Housing and green building guide lines also give higher priority to water efficient building service features.
Any commercial building is going to have air conditioning system to provide comfortable atmosphere to its occupants. The chart (next page)will give you the water chart of any commercial building.
Now, once the water requirement is clear, the designer or client has to submit water demand at Statutory Authority. Simultaneously, various options have to work out to use STP water, ground water and rain water harvesting, which we all know.
Now, let’s discuss, how we can save the water demand itself, which again has various sub categories such as:
• Defining fix and floating population.
• Proper calculation of domestic and flushing water requirement.
• Proper land cap irrigation and
• Of course water requirement for services.
All of us know that we should not do any compromise on fire fighting water requirement, but of course value engineering is required to reduce water requirement of air conditioning units.
As shown in the (next page) chart, Chiller Units needs a good quantum of potable water, the designer has to think various ways to tackle this issue. The services consultant has to take the first step on how to reduce the potable water requirement by a chilling plant of course with a techno-commercial comparison of availability and cost of water versus the same of electricity.
Reducing the heat load
The first step an MEP Engineer should do is to reduce the heat load. It will directly reduce electrical power consumption, and water demand. All the green building bodies always give priority to reduce heat load of the building.
Various ways to reduce heat load:
1. Roof insulation is the first on the list. Roof can be laid with brickbat coba waterproofing, screed, white China mosaic tiling and good SRA materials. Again it can be fully covered with PV (photo voltaic) cells, over head tanks, chilling units etc resulting in a U value of 0.21 W/cm.K.
2. Wall insulation was then added on all sides of the bedrooms, using 25 mm glass wool covered with Gypsum board.
3. Glass windows can be of double glazed sandwich type with a U value of 2.1 W/m.K.
4. The light fittings should be LED type fixtures.
Note: In each case several different materials have to be considered to evaluate the best alternative.
With all these measures the final heat load can be reduced up to 675 sq ft/ton, instead of 150 sq ft/ ton of normal practice. The reduction of heat load can help in reducing demand of potable water up to one fourth of the total requirement. In the same way, the total electrical demand of the building also gets reduced.
Source of water for services
Although domestic water has to come from municipal supply, where 100% guarantee is there for availability but rain water stored in a tank and STP water with proper treatment can be used for Cooling Tower but the cost is very high in both the options.
Selecting the AC system
Now that the plant capacity is determined, various options are considered, and a central chilled water system is selected for maximum flexibility.
1. Water Cooled VRV Units also save water demand compared to water cooled chillers with better power consumption benefit.
2. Air Cooled units (VRV and Chillers) can be fruitful, if requirement is less or when portable water is not available.
3. Geothermal Air Conditioning System stands first in the row. It uses ground water for air conditioning system.
4. Ground water cooled chiller Units are also good alternatives. Unused Bore well has a water temperature in the summer months of 260C maximum. Further cooling of this source of water to 80C through a small capacity water-cooled packaged chiller can give us the chilled water required for the Fan Coil Units in the air conditioning areas.
Water scarcity is a global problem, and we all designers and planners have to work together to sort it out. Air Conditioning engineer with good coordination with Plumbing Engineer can definitely save up to 25% of total water demand of a building.
AUTHORS CREDIT & PHOTOGRAPH
Firoj Kumar Jena
Clancy Global Consulting Engineers