Pressure

With these data and the well-known formula:

Being the flow rate, the speed, the area of ​​the straight section of the pipe and its diameter.

The section of the pipe and the diameter of each section are determined. The diameters thus obtained for the final branch sections to each device are very small. To avoid incrustations and possible obstructions, it is common to establish for these sections a minimum diameter of 12 mm in copper and plastic or ½” in ​​steel pipe for all appliances, except the bathtub, washing machine or dishwasher and industrial sinks, which will be made in 20 mm for copper and plastic or ¾” for steel pipe.

In the internal pipe network, the route is selected between the outlet of the pressure group and the most unfavorable device, generally the highest and furthest. The head loss of each section of this path is calculated analytically, or determined using a nomogram. The pressure loss of the route will be the sum of the losses in each section, to which the loss in accessories must be added, calculated from those existing in the section, or estimate it between 10 to 30%, depending on the accident rate of the section, of the linear head loss.

The necessary pressure at the outlet of the pressure group will be:.

Being:.

The pressure group to be installed must provide the maximum simultaneous flow or peak flow of the network, with an equal starting pressure.[12]​.

The inlet pressure is derived from the supply water pressure or from the existing pressure if the booster system is fed through a burst tank. The inlet pressure can be positive or negative. Negative inlet pressure usually occurs in cases in which the booster group must be fed from tanks located below the level of the pumps. If the inlet pressure is too small, NPSH will cause the pressure inside the pump to drop below the vapor pressure of the pumped liquid. As a consequence, the effect called cavitation occurs in the pump, causing noise and causing breakage.[13]​.

Whether the inlet pressure is negative or positive will influence the placement of the check valve. In the event that the inlet pressure is negative, the non-return valve must be placed before the pump in the direction of circulation, so that the pump is not empty of water during waiting periods. On the contrary, if the inlet pressure is positive, the valve must be placed downstream of the pumps, ensuring that the maximum pressure of the group is not transmitted to the supply network and that the pressure of the building's water column does not weigh on the pumps.

The stop pressure will be obtained by adding 100 to 300 kPa to the start pressure, depending on the size of the installation, from single-family homes to large residential buildings or public buildings with high consumption.

If at any time, the pressure necessary due to the height of the building could give rise to pressures greater than 500 kPa on the lower floors, pressure limiting valves will be installed at the entrance to said floors.

pressure tank

Pressure tanks or hydropressors can be of two types:

The calculation of the tank capacity is done using:[15]​.

Being:.

If the tank is to be installed with a group equipped with a frequency converter,[18]​ the size obtained with the previous formula can be divided by 4.

The necessary tank size can be calculated with the Boyle-Mariotte law, although a size equivalent to between 3 and 4 times larger than that obtained for the membrane tank can be considered.

Caudal

The estimation of the necessary flow has been done in different ways according to the regulations in force in each case. It was generally done with a prior classification of the consumption units into “categories” and assigning a fixed flow rate to each of them.[8]​

It was also done by estimating the consumption of each type of use: shower, bath, washing dishes, etc. and the number of users in each consumption unit and still in some, to refine the result, a correction coefficient was applied by social level.

These methods can continue to be used, which in some cases can support or help the estimate, but they imply too many assumptions, which logically are evaluated upwards, which generally results in a very oversized flow.

The option proposed by the DB-HS4 of the Technical Building Code in Spain,[9] seems to give more accurate results.

The values ​​given in the table are assumed to correspond to the capacity "Capacity (chemistry)") of the corresponding taps, both cold and hot water, under conditions of normal use.

The total flow rate in dm³/s will therefore be equal to the sum of the products of the number of equal units of each device, multiplied by the corresponding minimum instantaneous flow rate, taken from the table or, in the case of devices not included in the table, the nominal flow rate per second, indicated by the manufacturer.

However, the use of the devices is not simultaneous. The maximum flow for which the installation must be calculated will, therefore, be the maximum simultaneous flow. The number of devices that can most likely operate at the same time is obtained by means of a simultaneity coefficient. There are many formulas to obtain this coefficient, the simplest and also the most used, although perhaps too generic, is:

Where N is the total number of installed devices.

The flow will therefore be:

The UNE standard offers another formula, perhaps more adjusted, with which much lower flows are obtained than in the previous one[10]​ in addition to clearly differentiating the types of building, which seems more reasonable.

Being:.

Once the total flow is obtained, the flow section by section is calculated. Next, the circulation speed is determined, whose value is, with small differences, very similar in all the literature on the subject. In Spain, according to HS4, it must be between 0.5 and 2.00 m/s for metal pipes, and between 0.5 and 3.5 m/s for plastic pipes,[11]​ with the highest speeds for large diameters and the lowest for small diameters. A medium value, in both cases, has proven good results.

Pressure

With these data and the well-known formula:

Being the flow rate, the speed, the area of ​​the straight section of the pipe and its diameter.

The section of the pipe and the diameter of each section are determined. The diameters thus obtained for the final branch sections to each device are very small. To avoid incrustations and possible obstructions, it is common to establish for these sections a minimum diameter of 12 mm in copper and plastic or ½” in ​​steel pipe for all appliances, except the bathtub, washing machine or dishwasher and industrial sinks, which will be made in 20 mm for copper and plastic or ¾” for steel pipe.

In the internal pipe network, the route is selected between the outlet of the pressure group and the most unfavorable device, generally the highest and furthest. The head loss of each section of this path is calculated analytically, or determined using a nomogram. The pressure loss of the route will be the sum of the losses in each section, to which the loss in accessories must be added, calculated from those existing in the section, or estimate it between 10 to 30%, depending on the accident rate of the section, of the linear head loss.

The necessary pressure at the outlet of the pressure group will be:.

Being:.

The pressure group to be installed must provide the maximum simultaneous flow or peak flow of the network, with an equal starting pressure.[12]​.

The inlet pressure is derived from the supply water pressure or from the existing pressure if the booster system is fed through a burst tank. The inlet pressure can be positive or negative. Negative inlet pressure usually occurs in cases in which the booster group must be fed from tanks located below the level of the pumps. If the inlet pressure is too small, NPSH will cause the pressure inside the pump to drop below the vapor pressure of the pumped liquid. As a consequence, the effect called cavitation occurs in the pump, causing noise and causing breakage.[13]​.

Whether the inlet pressure is negative or positive will influence the placement of the check valve. In the event that the inlet pressure is negative, the non-return valve must be placed before the pump in the direction of circulation, so that the pump is not empty of water during waiting periods. On the contrary, if the inlet pressure is positive, the valve must be placed downstream of the pumps, ensuring that the maximum pressure of the group is not transmitted to the supply network and that the pressure of the building's water column does not weigh on the pumps.

The stop pressure will be obtained by adding 100 to 300 kPa to the start pressure, depending on the size of the installation, from single-family homes to large residential buildings or public buildings with high consumption.

If at any time, the pressure necessary due to the height of the building could give rise to pressures greater than 500 kPa on the lower floors, pressure limiting valves will be installed at the entrance to said floors.

pressure tank

Pressure tanks or hydropressors can be of two types:

The calculation of the tank capacity is done using:[15]​.

Being:.

If the tank is to be installed with a group equipped with a frequency converter,[18]​ the size obtained with the previous formula can be divided by 4.

The necessary tank size can be calculated with the Boyle-Mariotte law, although a size equivalent to between 3 and 4 times larger than that obtained for the membrane tank can be considered.