Hot climates and limited water supply

Hot climates and limited water supply

Water balance, control of salts and formulation of the annual operating budget

In a hot and water-scarce climate, the design of the fountain should begin with the knowledge of water sources, evaporation conditions and the ability to maintain the complex. Water recycling is an important part of the design; But a closed-circuit fountain also needs incoming water to compensate for evaporation, droplet exit, and necessary discharges.

In order to evaluate a plan, the amount of incoming water, the reason for the outflow of water and its quality must be known. A large flow rate of the pump does not necessarily mean a large intake from the network; Just as the smallness of the pond alone does not guarantee low consumption.

In this chapter, a hypothetical decorative water feature is investigated. The numbers are chosen to teach the calculation method and are not specific city climate data or measured performance of the GSO product.

51–1. Definition of water restrictions at the beginning of the project

Before choosing a spray pattern, the employer and the designer must come to a conclusion about four issues:

• authorized and sustainable source of water supply;

• acceptable ceiling of incoming water per day and year;

• Water quality and treatment needs;

• Activity plan during supply limitation periods.

The water budget should be considered along with the quality of the show. For example, reducing operating hours, reducing the free water surface and changing the shape of the spray have different effects on consumption, appearance and cost.

In the project specifications, it is better to convert the general phrase "low-consumption fountain" into measurable indicators; Such as compensation water volume, discharge volume and climatic conditions corresponding to them.

51–2. Educational sample specifications

24 cubic meter inventory includes pond water, pipes and equipment. This value is different from the flow rate of pump circulation or daily input water.

The zero assumption for leakage is the design objective and basis of calculation; Its realization must be confirmed by testing and monitoring.

Figure note from the source manuscript

Figure 51–1: Diagram of water routes

The water fountain should be placed in the center and the paths of compensation water, accepted rainfall, evaporation, droplet exit, washing, controlled discharge and possible leakage should be marked with arrows. The internal circulation of the pump should be displayed as a loop inside the system.

51–3. Three different values in the water report

Three concepts should be separated in the technical report:

Water availability: the volume of water that is inside the system at a moment.

Circulating water: the volume that the pump passes through the circuit in one interval and mainly returns to the set.

Inlet or make-up water: Water introduced from a supply source to fill or replace outlets.

Also, evaporated water is not the same as drained water. The drained water may, after checking the quality and the permission of the use, have the possibility of another use; Evaporated water is removed from the system.

Therefore, in this chapter, "water supply budget" refers to the volume of input. Evaporation volume and liquid output are also reported separately.

51–4. General water balance equation

For a given period of time:

$\Delta V=M+R-E-D-W-B-L$

in which:

• $M$ : compensation water;

• $R$ : Rainfall or other input that actually enters the system;

• $E$ : evaporation;

• $D$: dropping drops from the collection area;

• $W$ : water removed for washing;

• $B$ : additional controlled discharge;

• $L$: leakage and unwanted exits;

• $\Delta V$ : Inventory change.

If the balance at the beginning and end of the period is the same:

$M=E+D+W+B+L-R$

All values must be recorded for the same interval and with the same unit. Changing the water level without correcting the return volume from the lines or the condition of the pumps can distort the monitoring result.

51–5. Calculation of evaporation on a hot day

Free surface evaporation in the example:

$E_{surface}=Ae$

$E_{surface}=80\times 0.008=0.64m^3/day$

By adding the hypothetical evaporation caused by the activity of the effects:

$E=0.64+0.16=0.80m^3/day$

The number eight millimeters is an educational assumption. The actual value must be obtained from appropriate site data, a valid model, or measurement.

Evaporation from the meteorological pan, evaporation from the pond and plant reference evapotranspiration are not the same quantities. FAO also considers specific coefficients and conditions for the relationship between pan evaporation and reference evapotranspiration. FAO explanation about pan evaporation and evapotranspiration reference ^[332]

In this example, surface evaporation is considered for the whole day. Turning off the fountain does not reduce free surface evaporation to zero.

51–6. Why do solutes increase in the recycling circuit?

During evaporation, most of the dissolved solutes remain in water. Addition of compensation water also introduces new solutes into the circuit, depending on the quality of the source.

Conventional mechanical filtration does not remove all dissolved solids. Therefore, it may be necessary to drain part of the water or another purification process to maintain the required quality.

In evaporation systems, the concept of "concentration ratio" is used to express the ratio of circulating water concentration to incoming water:

$N=\frac{C_{system}}{C_{makeup}}$

US Department of Energy guidance explains this balance for cooling towers. In this chapter, only the principle of survival of water and dissolved matter is used; Chemical limits and cooling tower maintenance methods are not water fountain instructions. Water balance and concentration ratio in DOE guide ^[333]

51–7. Extracting the required discharge from the solute balance

For the training model, we assume:

• The water in the system is completely mixed;

• Evaporation does not remove the component of the investigated solution;

• Droplet output and washing water have the concentration of system water;

• There is no sedimentation, reaction, precipitation and entry of matter from other sources;

• Conditions are almost stable.

With zero leakage, the solution component equilibrium:

$M{C}_{makeup}=(D+W+B)C_{system}$

So:

$M=N(D+W+B)$

From the water balance:

$M=E+D+W+B$

By combining two relations:

$D+W+B=\frac{E}{N-1}$

And as a result:

$B=\frac{E}{N-1}-(D+W)$

In this example, $N=3$ is only a calculation assumption and not a water quality limit.

$B=\frac{0.80}{3-1}-(0.04+0.06)=0.30m^3/day$

Compensation water:

$M=0.80+0.04+0.06+0.30=1.20m^3/day$

Therefore, for this hypothetical day, it is necessary to supply 1200 liters of water.

If the relationship gives a negative extra discharge, the negative discharge has no meaning; Existing departures for the target ratio exceed the required value and the actual conditions should be re-examined.

51–8. Selection of water quality limits

The allowable concentration ratio should be determined by the quality of the source, materials, equipment and water management plan. A single number is not suitable for all fountains.

Electrical conductivity can be useful for tracking solute changes, but is dependent on temperature and ionic composition. Its use as a proxy for concentration ratio requires investigation and calibration.

In this project, the water quality file must specify:

• Which parameters are limiting;

• Where and how sampling is done;

• What conditions need to be corrected or stopped;

• Which way is the discharged water allowed to go?

Solvent control is not a substitute for microbial control. In managing decorative fountains, the CDC also emphasizes temperature, biofilm, water retention, and residual disinfection. CDC Decorative Water Fountain Management Guide ^[334]

51–9. Real-time cost savings from sprinkler control

Wind control and height adjustment can limit the droplet exit from the pond. Otterbine also introduces wind-dependent lowering and stall controls for some of its sets. Otterbine Wind and Water Level Controls ^[335]

However, the savings must be calculated from the full balance.

If only droplet output is reduced from 0.04 to 0.02 cubic meters per day and evaporation and concentration ratio remain constant:

$B=\frac{0.80}{2}-(0.02+0.06)=0.32$

$M=0.80+0.02+0.06+0.32=1.20$

In this model, the decrease in droplet exit is compensated by increasing the controlled discharge, and the inlet water does not change. Despite this, peripheral drying and splash reduction are still advantageous.

Now let's assume that the new setting also reduces the added vaporization of effects from 0.16 to 0.08:

$E_{new}=0.64+0.08=0.72$

$B_{new}=\frac{0.72}{2}-(0.02+0.06)=0.28$

$M_{new}=0.72+0.02+0.06+0.28=1.08$

Reduction of incoming water in this scenario:

$1.20-1.08=0.12m^3/day$

That is 120 liters per day. This result depends on the assumptions of the example and must be measured in the implementation.

Figure note from the source manuscript

Figure 51-2: Comparison of three operating conditions

Three columns should be drawn for the base case, the reduction of droplet emission alone, and the simultaneous reduction of evaporation and droplet emission. The contribution of evaporation, washout, droplet exit and controlled discharge are displayed with separate colors.

51–10. Adjust design for hot climates

To reduce water demand, options should be compared from the architectural stage:

The effect of none should be declared as a fixed percentage of savings without investigation.

Shading and covering should also be compatible with structural load, cleanliness, safety and visual quality. Changing the shape of the architecture may also change the circulation of air or the accumulation of pollution.

51–11. Instrumentation and compensatory water control

The minimum information required to manage this example is:

• volume of incoming water;

• The volume of measurable discharges;

• water level;

• Effect activity status;

• Weather conditions and water quality control results.

In the WaterSense Guide, EPA introduces differential metering as a tool to identify consumption and detect unusual patterns. EPA Measurement and Submetering Guide ^[336]

GSO has also introduced water level control equipment to regulate the inventory and proper operation of the equipment. In this project, level control should be designed along with inlet volume monitoring. GSO level sensor and control equipment ^[337]

Automatic filling can hide the decrease in level caused by leakage. Therefore, filling time, cumulative volume and valve status should be seen in the alarm logic. The constant water level alone is not a sign of the absence of waste.

51–12. Alternative resources and reuse

Stored rainwater, distilled water from the ventilation system, or recycled water may be considered for some projects. Their suitability depends on the quality, usage of the water fountain, possibility of contact and maintenance conditions.

For each source, these questions must be answered:

• What is the reliable amount of supply in the required season?

• What purification and monitoring is required?

• How does the system work when this resource is not available?

• What effect does the storage tank have on water quality?

• How is its connection to the water network of the building protected?

Reducing withdrawals from the network does not necessarily mean a reduction in total water intake or maintenance costs.

For drained water, use in irrigation should not be default; The solutes, substances in the water and the requirements of the place of consumption should be checked. Rainwater is deducted from the incoming budget only if it is actually collected, accepted and consumed.

51–13. Annual estimate of water supply

For the initial budget, we divide the year into four hypothetical periods. In active periods, the concentration ratio of three and the quasi-steady model of the previous section are used.

The volume unit is cubic meters per day. The unloaded state assumes the annual schedule of this example.

$M_{annual}=90(1.20)+150(0.675)+90(0.30)$

$M_{annual}=236.25m^3/year$

If it is necessary to fill 24 cubic meters once during this period:

$M_{budget}=236.25+24=260.25m^3/year$

This budget does not model transient changes after recharge, effective rainfall, and excess cleanup water or unusual repairs. For performance contracting, daily data and a more accurate model are required.

The annual evaporation volume of this scenario is also equal to:

$E_{annual}=90(0.80)+150(0.45)+90(0.20)=157.5m^3/year$

Figure note from the source manuscript

Figure 51-3: Water budget calendar

Four periods of the year with the number of days and the volume of compensated water should be displayed. Initial or seasonal filling should be placed in a separate row so as not to be confused with the daily make-up water.

51–14. Supply restriction period program

The project must have defined its allowed states before the limitation occurs.

Reducing display hours should not result in the suspension of an essential water management program without review.

The architecture of the water fountain is also better when it is turned off, it has an acceptable appearance and can be maintained. This is part of the design quality for a project that may have limited activity for part of the year.

51–15. Performance test and detection of loss

For evaluation, activity periods should be checked with simultaneous recording of weather conditions, state of effects and input volume.

A test program can include the following steps:

1. Checking the sealing and recording the behavior of the surface under controlled conditions; 2. Measuring the return water after stopping the pumps; 3. Registration of compensatory water and discharge during the specific activity period; 4. Implementation of limited mode and comparison under similar conditions as possible; 5. Balance control in terms of inventory changes; 6. Unexplained dispute investigation.

A balance difference should not immediately be called a "leakage"; Instrument error, unrecorded departures, rainfall and inventory changes should also be investigated.

The savings claim must include the baseline, test period and comparison conditions. Comparing a cool and calm day to a hot and windy day alone does not show the effect of equipment modification.

Figure note from the source manuscript

Figure 51–4: Actual tracking from company archives

Select the image of the compensatory water meter, the level sensor and a sample of the daily record sheet. The subtitle should include the name of the project, measurement location and recording interval. The hypothetical numbers of this chapter should not be introduced as the performance of that project.

51–16. Study results and delivery documents

The final documents should specify the supply source, water budget, quality limits, discharge route, measurement points and supply restriction schedule. After setup, evaporation and transpiration assumptions should be corrected with actual data.

For the municipality or the operator, a reliable report is a report that shows how much water was imported, what part was evaporated or drained, and what effect the program change had. Such a report will be the basis for decision about operating hours, equipment modification and maintenance cost.