Kitabı oku: «Water and Energy Engineering for Sustainable Buildings Mihouse Project», sayfa 2

Prototype Scale

Figure 1.2. Prototype Scale

Note: Process of post-war reconstruction

Source: The Autors.

The project Mihouse constructive system is based on the prefabrication of prestressed concrete structural elements, recognized advantages in the construction of mass housing at reduced costs and widely used in many experiences in our country. On the other hand, the seismic condition of Cali, located in the western region of Colombia, which is part of the so called “Ring of Fire”, known worldwide for its high probability of major earthquakes, requires the construction of buildings with high resistance to such natural events and precisely with material that provide the proposed structural safety system required in these cases (Figure 1.2).

This criteria, paired with the high sustainability of the chosen materials and the principles of constructive and structural efficiency, has hallowed to propose the Mihouse project as a building that can be shaped primarily by two prefabricated structural modules in prestressed concrete. These concrete modules can be conveniently repeated and assembled together and they define the spatiality of the housing units and the number of floors required for the technical feasibility of the proposal.

For identification, we have given the name “Main Table” and “Central Table” at Figure 1.3.

Figure 1.3. Main Table and Central Table

Main Table - Central Table

Source: The Authors.

Resting on a foundation of reinforced concrete plate, which must be designed according to the type of terrain that applies in each case, the main structure of the building is resolved as a stack of these basic structural modules, linked together by mechanical fasteners that provide and ensure its comprehensive action to support vertical loads and horizontal seismic forces. Along with a perfect assembly of the constituent parts, this new system excludes the need to dry joint, which is one of the most critical points in the traditional way as usually these structures are resolved.

The following Figure 1.4 shows the design of the prototype of the apartment located at the top floor of the building at the residential condominium, the process of assembly of this house would be first the junction of the modules shown in Figure 1.3 through high resistance mechanical anchors, then the installation of the ramp, steel orchard, Teak wood blinds, the green wall structure and the plastic wood deck, would be made forming the residence shown in the Figure 1.4.

Figure 1.4. Mihouse Prototype design

Source: The Authors.

In addition to the residence prototype, the following sequence shows the assembly of the modules up to the completed building, and conceptually illustrates high construction efficiency of the proposal.

Figure 1.5. Assembly of the modules up to the completed building.

Source: The Authors.

Wall lengths resulting in each orthogonal direction of structural plant generate a high regularity in response to earthquake resistant assembly being confluent in perfect symmetry and the center of mass and rigidity, thereby providing high reliability in evaluation of earthquake resistant building in the light of the rules required by the Colombian Earthquake Resistant Building Regulations NSR-10, mandatory in our country (Figure 1.5).

Chapter 2
Water Management System

Daniel Mauricio González Naranjo¹

Alejandro Beltrán Márquez¹

Javier Eduardo López Giraldo¹

Jeffer Steven Mosquera Castillo¹

Juan Pablo Trujillo Chaparro¹

Nicolás Noreña Leal¹

Javier Ernesto Holguín González²

System Design

In this project we considered the rational use of natural resources; therefore, our proposal is to have an integrated water management system that allows us to have sustainable solutions such us: (1) to reduce the consumption of drinking water; (2) to treat and to reuse the greywater for flushing the toilet; (3) rainwater exploitation. In the following section, the strategies for each element of the plumbing system design are described.

The plumbing system is composed by four main components:

• Water tanks: composed by 66 tanks (2 underground drinking water tanks, 2 underground greywater tanks, 60 elevated rainwater tanks and 2 underground rainwater tanks),

• Pumping system: composed by 6 pumps (2 for taking the water from the underground drinking water tanks to the utilities, 2 for taking the water from the underground rainwater tanks to the irrigation system and 2 for taking the water from the greywater tanks to the toilets),

• Conduction and discharge pipes (for hot and cold drinking water, rainwater, greywater and black water),

• Greywater treatment system and drinking water meters.

Design Criteria

The criteria considered for using and reusing water was developed based on an objective, which is the adoption of alternative sources of water. In the following paragraphs a detailed description of the water storage tanks, and the plumbing system considered in the technical proposal for Mihouse project is presented.

Water storage tanks – Rainwater. In general, a rainwater exploitation system for domestic use should have three main sub-systems, a rainwater collection sub-system, an interceptor sub-system and a storage sub-system. These three main sub-systems are composed by several elements such as: a) roof’s catchment, b) collection by gutters and downspouts, c) a first flush rainwater interceptor, d) storage tanks, e) a physical treatment unit and, f) a distribution system.

The use of rainwater in this project aims to satisfy the basic needs of the people living in these apartments related to the use of non-potable water (washing floors, watering of plants and so on). Our proposal consists of two elevated storage tanks which are located on top of the roofs and that will be fed by a system of gutters. The rainwater collected in these tanks is afterwards conducted to each apartment. Additionally, the water which is not collected in the storage tanks is drained to the 2 underground rainwater tanks.

The capacity of the two elevated storage tanks is 216 liters. Each of these tanks has the following dimensions: 0,30 cm high, 0,60 cm wide and 0,60 cm long. It should be emphasized that the storage capacity varies because part of the water can be stored along the pipeline or it can decrease due to evaporation of the water. The rainwater collected in these tanks is conducted by gravity to each apartment through a pipe of ½ inches and it may be supplied by a tap located 30 cm above the floor just below the sink and next to the laundry machine.

Each of the buildings has this exploitation system for the rainwater. This system will allow people to reduce water consumption. The total storage capacity associated with elevated tanks is about 6480 liters, distributed in 60 tanks, 2 tanks in each of the 30 buildings of the residential complex.

Technical and Economic Factors. From the technical perspective, it should be considered the water demand and the water availability, which is closely related to rainfall during the year and the seasonal variations of it. So, it is essential to work with the rainfall information provided by the competent authorities at the time of designing the catchment system. Moreover, due to the water demand and water availability by rainfall there is a direct relationship between supply and demand for water, which defines the size of the catchment area and the storage volume. Both considerations are intimately connected with the economic aspects, which may preclude access to a collection system of this type.

The implementation of a groundwater system involves knowledge about the type of soil, nearby sources of pollution, large machinery and infrastructure cost. Moreover, it is necessary a rational use of groundwater because an excess of demand could affect the natural ability of the system to recharge.

System components

• Rainwater Catchment: The area where the project is located has a direct relation with the possible rainwater harvesting. The catchment system is implemented in the roofs of the buildings, by using gutters, tiles, etc.

• Interceptor and rainwater driver: It is a fundamental part of the system collecting rainwater, they are responsible for driving the collected water to the storage tank.

• Collection and conduction gutters: Gutters are accessories to collect and to conduct storm water runoff to a storage system; its dimensions are a function of the duration of precipitation (short and homogeneous), the water concentration time, the length of the passage area and its slope.

In a catchment area, the water concentration time is a fundamental parameter in the hydrological study of a watershed and runoff areas with slope. This time is described by mathematical expressions which, considering physical characteristics of the catchment area or basin, can provide a resultant hydrograph.

Below, are shown the equations for determining the gutter flow transported, depending on the precipitation time, draining and other factors:

1. In order to calculate the concentration time (tc), we used the Kirpich’s formula:

where: S: is the average slope; L: is the length of the catchment area in meters; tc: concentration time in hours.

2. Time in which the maximum runoff is reached in the basin or catchment area (tp):

where: D is the duration of effective rainfall in hours.

If the duration of daily maximum precipitation is unknown, the following equation is used:

3. Concentration Time of the maximum flow (tb). It is estimated for draining all the surface runoff from impervious catchment area, it is estimated by the following equation:

4. The maximum Flow (Qp). The maximum flow expected to net precipitation in the draining area is estimated by the following expression:

where: P is the effective precipitation (mm); A: catchment area (km); 0278: conversion factor (m³/s).

5. Estimation of the gutter area. The water that flows in the conduction gutters behaves as a spatially varied flow, because this water is gradually collected over of the gutter. In order to determine the required conducting area, we used the continuity equation, in which only the area is unknown and average speeds of 0,9 m/s on slopes 2-4 % and 1,2 m/s on slopes 4-6 % are assumed.

where: Qp: channel flow (m³ s); V: Gutter flow velocity (m s); A: cross sectional area (m²).

6. Storage volume (VA). The required volume for storing rainwater (VA), is given by the difference between the accumulated rainwater available (OA) and the accumulated water demand per month (DAM’) (Eq. 7). The highest value of (VA) is the value adopted for the tank volume. If (VA) has a negative value; it means that catchment areas are not enough to satisfy the rainwater demand.

where: VA: storage volume for the “i” month (m³); OA: accumulated rainwater offered for the “i” month (m³); DAM’: accumulated rainwater demand for the “i” month (m³).

7. Accumulated Offer (OA). It is given by the following equation:

where: OA: accumulated offer for the “i” month (m³); OA’: previous month accumulated offer “i-1” (m³); OAMP: accumulated offer for the “i” month considering losses (m³).

The accumulated offer per month (OA) will be included in the equation 7 and thus we can determine the storage volume for the rainwater collection system.

8. Water offer in a month (OAM). Considering the average monthly rainfall during the evaluated years, we proceed to determine the quantity of rainwater collected per month.

where: OAM: rainwater offer in the month “i” (m³); P: average monthly precipitation (l/m²); C: runoff coefficient (0,9); A: catchment area (m²).

In order to find the rainwater offered of the month considering the losses (OAMP), it is necessary to estimate the rainwater available during the month (OAM), both terms are used in Equation 10. It is noteworthy that the runoff coefficient in the Mihouse project takes the value of 0,9, because it is associated with metallic surfaces, which do not resist the flow direction. This feature matches the characteristics of solar panels on the roof of the buildings and the prototype house, moreover, it is important to note that the catchment area is function of the roof surface of the buildings, which in the urban complex consists of three different models.

9. Month Offer “i”, considering losses (OAMP). According to Abdulla and Al-Shareef (2006), one can assume a value of 20 % of annually rainwater losses because of evaporation, the storage and an inefficient collection system. For this reason, the volume of the available supply is affected for that percentage. This will prevent oversize the system and include in the design related losses.

where: OAM: rainwater offer in month “i” (m³); OAMP: Accumulated offer of the month “i” considering losses (m³).

10. Pluviometric information. In order to design the rainwater exploitation system, we should have the rainfall information in the study area, and it should be at least from ten consecutive years. With the obtained daily data, the monthly average precipitation is estimated, in accordance with Equation 5. With these results, we can analyze if the available rainwater is enough to implement a system to capture rainwater to fulfill the necessities of the project. Furthermore, the equation 11 is employed for obtaining Ppi which will be necessary to develop Equation 9.

where: P: monthly precipitation average (l/m²) of the “i” month evaluated every year (mm/month); n: number of evaluated years; Pi: Monthly precipitation value “i” (mm).

11. Water catchment coefficient. The efficiency of the rainwater catchment depends on the runoff coefficient of the materials used for the catchment area, which varies from 0,0 to 0,9.

12. Monthly Water Demand (DAM). The water demand can be estimated in several ways, the most common is by using the water endowment assumed by a person or the used for irrigation. This method calculates the amount of water needed to meet needs in each month.

Where: DAM: Monthly demand (m³); Dot: water endowment (l/irrigation/day) (2l/m²); N: total irrigation area; N: number of days in the analyzed month u d.

13. Accumulated demand per month (DAM’). It is determined by the expression proposed by Abdulla and Al-Shareef (2006). The (DAM’), is introduced in Equation 7 in order to determine the volume of the storage tank for rainwater.

Where: DAM’: accumulated demand per month “i” (m³); DAM: Month water demand (m³); DAM (i-1): accumulated demand from the previous month (m³).