Grading maintainability parameters for sanitary-plumbing system for high-rise residential buildings

M.Y.L. Chew, Dept. of Building, School of Design and Environment, National University of Singapore

(email: bdgchewm@nus.edu.sg) Sutapa Das,

Dept. of Building, School of Design and Environment, National University of Singapore (email: sutapa@ns.edu.sg)

Nayathara De Silva, Department of Building Economics, University of Moratuwa

(email: endds@becon.mrt.ac.lk) Foon Fong Yee

Dept. of Building, School of Design and Environment, National University of Singapore (email: foonfongyee@dpa.com.sg)

Abstract

Sanitary-plumbing system can waste energy and even become a source of fatal contamination unless designed, constructed or maintained properly. Human health and convenience are the two critical issues and it is important to identify, analyse and quantify the maintainability parameters of complex sanitary-plumbing systems to meet requirements of today’s bigger and better buildings. This research was undertaken to investigate the common defects in sanitary plumbing system in high rise residential buildings and their causing factors which may be the critical maintainability parameters of sanitary-plumbing systems. From the detailed case studies of five residential buildings in Singapore, a total of 113 defects were identified for ten major components of sanitary-plumbing system. Out of them 56 were graded as significant by 33 experienced facility managers based on frequency of occurrence and their adverse effect on: economy, system performance, environment and health. Poor maintainability consideration in design stage was apparent from the comprehensive defect analysis. The defect commonly found in almost all the components was the “inaccessibility” for regular inspection and maintenance.

Keywords: Contamination, Defect analysis, Maintainability, Sanitary-plumbing, System performance.

1. Introduction

Apart from wasting precious energy and water, sanitary-plumbing system can become a source of fatal contamination unless it was designed, constructed and maintained properly. With time the concept of maintenance has changed from the action of “breakdown repair” to “preventive maintenance”. Only clean water with quality hygienic standard is considered satisfactory.

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Hence this system deserves a keen attention particularly in Singapore as abundant rainfall, high temperature and humidity, coupled with high population density can cause waterborne diseases to spread easily and quickly unless a high standard of public health is maintained [1]. In a recent survey conducted by Hassanain [2], design professionals of nine countries have proposed 41 design guidelines with an emphasis on occupant’s health to a great extent.

Codes of practise, standards of design and operation handbooks have clear and well-defined guidelines for design and construction of sanitary–plumbing systems in general [1,3-5], along with detailed consideration for certain major issues such as piping [6], valves [7], pumps [8] and life cycle costing [9] etc. Yet major problems are reported frequently, all round the world such as leakage resulting in water scarcity [10], sewage contamination of potable water causing sickness [11] or recurrent cases of Legionella [12]. The root cause of many of these problems is derived from corrosion and wearing off of metallic parts which are common in pipelines, particularly in the consumer's plumbing fittings. Corrosion favours bacterial growth, developing high concentration of lead and copper components within the system and leading to dirty and contaminated water [13]. Researchers have drawn attention to various problems related to sanitary-plumbing system, such as lead contamination [14], biofilm formation [15] etc.

In most cases the solutions for a particular issue were seldom well communicated as a design, construction or maintenance guideline. Health and convenience are the two major critical issues, and it is not only important to identify and solve various defects, but it is equally essential to quantify and grade the maintainability parameters especially when qualitative decision making process is inadequate for complex sanitary-plumbing systems to meet the requirements of today’s bigger and better buildings. To address the absence of such grading system, this research was undertaken to investigate the types of defects that are commonly occurring in sanitary plumbing system in high rise residential buildings and to identify the significant ones.

2. Research methodology

2.1 Data collection

In order to obtain a preliminary idea of common maintenance problems in sanitary–plumbing system, major components were examined in a systematic site investigation process. In the first phase of data collection, an in-depth field survey was conducted in five residential towers to identify the common defects occurring in each major component. Discussion with facility managers (FM) and maintenance personnel was followed by expert on-site inspection. Comprehensive photo of each component parts were taken to investigate elements such as the fixture and fittings in individual toilet units, water storage tanks and pumps etc. The defects were diagnosed with the help of information provided by FMs, maintenance records of the buildings and the knowledge gained through the literature review [16-23] were elicited.

From the defect analysis, it was observed that a defect can cause adverse effects on (1) economy, (2) system performance; (3) indoor environmental quality (IEQ); and (4) occupants’

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health and well-being. These factors contribute to the level of seriousness of a defect A frequent defect might not have significant effect, whereas a very serious defect may happen once in a lifetime. For example, a slow discharge rate of supply water is common but it may not have as much impact on the user when compared with the contamination of potable water from sewage which may cause serious illness. Therefore apart from the frequency of occurrence, the following four major impacts were also considered to be the significant factors caused by the sanitary-plumbing system defects. :

• Economic loss: accumulated financial loss in long term due to the result of the defect. For example, high consumption of electricity due to wrong design resulting in excessive pipe length and bending leading to energy loss of hot water before discharging through the taps.

• System performance loss: such loss occurs when the system performs significantly below normal operating efficiency. For example, slow or disrupted sewage pumping system choked by solid waste discharge.

• IEQ loss: This loss originated from the defect that causes deterioration of the built environment. For example, due to trap seal loss, foul air from the discharge pipes or stacks enters into the building.

• Human health loss: affects the health of the building occupants and maintenance personnel as a result of the defect. For example, illness caused by Legionella contaminations in water supply system.

The defect data related to major components and sub-components of sanitary-plumbing system was collated in a detailed survey questionnaire. In a face to face interview, 33 experienced FMs were asked to indicate the frequency of the defect in a five point Likert scale, where, 1 = ‘rare’, 2 = ‘sometimes’, 3 = ‘quite often’, 4 = ‘very often’ and 5 = ‘always’. In order to estimate the impact of each defect, the respondents were asked to indicate the significance of the defects in terms of four consequences also in a five point Likert scale, where, 1 = ‘negligible’, 2= ‘slight’, 3 = ‘moderate’, 4 = ‘serious’ and 5= ‘very serious / fatal’. Among ten major components, the questionnaire for sanitary piping is shown in Appendix A as an example.

2.2 Data analysis

Mean ratings for the level of seriousness of the defects were calculated from the feedback received. Mean rating for frequency was defined as X FR, while the same for four impacts, namely, economic loss, system performance loss, IEQ loss and health loss were denoted by XEC, X SP, X EN and X HW respectively. For each defect, the vales were calculated by a general formula (Equation 1). Using statistical tool SPSS 12, T-test was carried out to identify the significance of each mean. The midpoint test value of 3 (by definition) was assigned to measure whether the defects have a significantly large enough mean with p<0.005.

∑∑ ==×=

5

1

5

1 X occurrence offrequency Mean

l il i nni (1)

Where, i = frequency rating.

ni = number of responses for i-th rating

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3. Results and discussion

3.1 General observation

For water supply, in most of the condominiums or public housing in Singapore, a gravity supply system was observed whereas hot water is supplied mainly from heater of individual residential units. Tankless type instantaneous heater is commonly installed for shower unit where no hot water is provided for lavatory and kitchen sink. For sanitary works, ventilated stack is used for all buildings with a height more than six stories. The wastewater is collected and conveyed by combined sewers to sewage treatment works before final discharge into the sea. In general it was found that many defects occurred due to poor design consideration for maintenance. The access to various components or provision of work space for maintenance is inadequate. In concealed pipe work, it is difficult to determine the exact location and root cause of any fault. It was also observed that one defect may give rise to a chain of defects. For example, corrosion of piping may cause leakage, which in turn results in water ponding, backflow of dirty water from surrounding soil, as well as wastage of water.

3.2 Survey results

The summary of survey results is presented in Tables 1 - 6 for water supply, while Tables 7 -10 illustrate the prevalent defects in sanitary system. A total of 113 defects related to ten major components of sanitary-plumbing system were identified, out of which 56 were found serious and among those 13 were referred by FMs as frequent and 17 occurs in two or more categories. Economy, system performance, IEQ and health & well-being were affected by 40, 34, 9 and 20 defects respectively. All the significant defects for ten major components are graphically illustrated in the defect list (Tables 1-10). As an example, defects in sanitary piping are discussed in details in Section 3.3.

Table 1: A summary of the defects in supply main

Sub component

Common defects (11 nos.)

Seriousness of significant defects (3 nos.)

Piping Overflow, contamination, slow discharge / backflow, hydraulic thrust, dirt accumulation at dead end, less supply, leakage, damage

2 2.5 3 3.5 4

X FR X EC X SP X EN X HW

Stop Valve Unable to cut supply for repair

890

Air valve Air lock at high point (low pressure flow), Air gap at summit (normal flow)

Table 2: A summary of the defects in service pipe

Sub component

Common defects (18 nos.)

Seriousness of significant defects (11 nos.)

Underground pipe

Settlement, damage due to settlement

2 2.5 3 3.5 4

X FR X EC X SP X EN X HW

Exposed pipe Corrosion, other degradation

Internal pipes Leakage, contamination, air locks, slow discharge, noisy flow, dirt accumulation, supply-discharge interference, damage (thermal stress), poor accessibility, difficult to locate, difficult cleaning

Valves In-accessibility, supply suffers during repair

Fittings Corrosion

Table 3: A summary of the defects in over-head / under-ground storage

Sub component

Common defects (14 nos.)

Seriousness of significant defects (11 nos.)

Tank body Corrosion, leakage, poor / no ventilation, flooding around tank, clogged wash out pipe

1.5 2 2.5 3 3.5 4 4.5

X FR X EC X SP X EN X HW

891

hinders cleaning

Intake Overflow, interruption, back siphonage, stagnation / short circuiting

Discharge Contamination, level goes below pipe invert

Controls Faulty valve, alarm indicator etc

Accessory Corroded net or strainer etc, entry of dirt or insect

Table 4: A summary of the defects in distribution pipe

Sub component

Common defects (14 nos.)

Seriousness of significant defects (7 nos.)

Underground piping

Settlement, damage due to settlement, mechanical damage, leakage

2 2.5 3 3.5 4

X FR X EC X SP X EN X

HW

General Contamination, degradation, low discharge rate, air locks, frictional loss, head loss at bend / joint, noisy flow, ugly arrangement

Valves In-accessibility, supply suffers during repair, corrosion of components

892

Table 5: A summary of the defects in hot water supply

Sub component

Common defects (8 nos.)

Seriousness of significant defects (5 nos.)

Piping Wastage of water, heat loss, short circuiting in the piping of the primary and secondary circuit, scaling, Legionella growth, corrosion

2 2.5 3 3.5 4

X FR X EC X SP X EN X HW

Tank Corrosion, bursting

Table 6: A summary of the defects in pumps

Sub component

Common defects (9 nos.)

Seriousness of significant defects (3 nos.)

body Corrosion 2 2.5 3 3.5 4

FR EC SP EN HWImpellers Corrosion, out of balance

Valves Damaged reflux and isolating valves

Controls Faulty control can’t auto interchange duty and standby pumps after each cycle of operation.

In general Damaged pumps, choking, over heating, excessive vibration

Table 7: A summary of the defects in sewage ejector or solid diverter tank

Sub component

Common defects (8 nos.)

Seriousness of significant defect (4 nos.)

Tank / pit Poor accessibility for maintenance, poor working condition, inadequate ventilation,

2 2.5 3 3.5 4

893

vandalism / break in, water penetration / ponding, corrosion

X FR X EC X SP X EN X HW

Air compressor

Incomplete sewage discharge

Sump pump Unable to dewater

Table 8: A summary of the defects in sewage pumps

Sub component

Common defects (5 nos.)

Seriousness of significant defects (2 nos.)

Body Corrosion 2 2.5 3 3.5 4

X FR X EC X SP

X EN X HW

Impeller Corrosion, out of balance

Controls Unable to auto interchange of duty and standby pumps after each cycle of operation.

General Long fibrous materials of raw sewage cannot be pumped (clogging), solids of diameter ≥ 64mm diameter cannot be pumped (choking)

Table 9: A summary of the defects in sanitary piping

Sub component

Common defects (10 nos.)

Seriousness of significant defects (7 nos.)

General Corrosion, leakages, slow discharge , no discharge, discharge of foul air into the building, poor accessibility for maintenance and repair, contamination , trap seal loss,

2 2.5 3 3.5 4 4.5

X FR X EC X SP X EN X HW

894

mosquito breeding in open trap, noisy flow

Table 10: A summary of the defects in sanitary fixture and fittings

Sub component

Common defects (13 nos.)

Seriousness of significant defects (3 nos.)

WC pan Water ponding around pan, discharge pipe disconnected from pedestal type pan, collapsed / dislodged of support brackets of wall-hung WC

2 2.5 3 3.5

X FR X EC X SP

X EN X HW

Flushing Cistern

Leakage of water and air at the connection of flush pipe and WC pan, damaged device no longer automatic

Urinal Clogged trap

Bidet Backflow or back siphonage

Bath and shower unit

Leakages at the joints at the edge of wall and tray, poor maintenance of the waste pipe / trap under the bath

Floor trap Slow drainage

Grating / cover for floor trap / waste

Corrosion, damaged gratings causes undesirable opening and penetration of garbage or other solid waste

Accessory Corrosion of installation screws

3.3 Discussion

For three sub-components of sanitary piping, a total of ten common defects were identified from the first phase of data collection, among which none was frequent but seven were found to be significant for their impacts. Such piping seldom suffers from leakage, but it causes

895

considerable amount of economic loss. This may be due to the corrosion of structural members initiated by water leaking through the joints of concealed pipes. Slow discharge is an example of system performance loss, but no discharge incurs huge cost as the trap or pipe that may require replacement. Though discharge of foul air into the building due to trap seal loss is a well discussed topic but it is considered insignificant from FMs’ point of view. On the contrary, poor accessibility for inspection, cleaning and repair was reported as a major hurdle for maintaining proper IEQ. Contamination as caused by backflow and back-siphonage i.e. major defect of design or construction was considered expensive as replacement is the only remedy. Similarly mosquito breeding in open traps was found to have the highest emphasis for health and well being among all 113 defects as this may cause fatal Dengue fever to spread. For the same reason, this defect was considered to be a great expense on FM as failing to rectify this defect may incur huge penalty. Noisy flow as caused by interrupted discharge is an unpleasing example of system performance loss, often demanding costly cleaning or replacement.

From the present study, it was established that among many defects in sanitary-plumbing system, most of the defects can be prevented by considering four major maintainability criteria, namely, design, appropriate material selection, construction practices, and operation & maintenance (O&M) practices and few defects have more than one cause.. It is important to know at which stage what are the defects arise so that the appropriate preventive measures can be taken to improve the maintainability. It was found that among 56 significant defects, 38 are design related, 14 occurred due to poor material selection, 16 were due to bad construction quality and inadequate O&M practises were responsible for 19 defects. Especially poor accessibility for regular inspection, cleaning and routine maintenance was found to be one of the major and prevalent defects which can be addressed during the design stage.

4. Conclusions

The study had identified 56 persistent defects out of total 113 defects commonly occurring in ten major components of sanitary-plumbing system. The inaccessibility for regular inspection and maintenance was detected as the common defect for almost all the components. From the analysis based on feedback provided by 33 experienced FMs regarding: (1) frequency of occurrence of various defects and (2) seriousness of the defects in terms of their adverse effect on economy, system performance, indoor environmental quality and occupants’ health & well-being, it was established that the most important contributing factors for maintainability is good design, next comes by O&M practices, followed by construction quality, and material selection. This comprehensive defect analysis was aimed to help the designers, contractors and facility managers to realize the long term effect of their decisions made and form the basis of an enhanced maintainability to promote good practices for efficient and safe functioning of highly maintainable sanitary-plumbing system. Further, this may provide a simple guideline for FMs to achieve and as well as owner to enjoy lower life cycle maintenance cost of building services. This generic research method can be applicable for any other building services.

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APPENDIX A: Sample questionnaire for sanitary piping

Defects for sanitary piping Grading for Frequency

Grading for Impacts

Sub-compo-

nent

Description of Defect

Probable Causes of the Defect

1= Rare 2= Sometimes 3= quite often 4= very often 5= Always

1 = Negligible 2= Slight 3 = Moderate 4 = Serious 5= Very serious / fatal

Economy

Sys. Perf.

IEQ Health

Piping

Corrosion Deterioration over time, piping material is not corrosion resistant or unsuitable for pumped media

Leakages Corrosion, joining pipes of different material, absence of elastomeric seal at joints or sleeve at slab / wall penetrations

Clogging (slow /no discharge)

Dirt entering through damaged / removed floor trap or solid construction waste causes clogging in pipes

Noisy flow Interrupted flow (bad design of pipe-trap connection)

899

Discharge of foul air into the building

Non provision / wrong design of ventilating pipe, trap seal loss of fixtures

Poor accessibility for maintenance

Mismatched position of access cover / cleaning eyes and pipe joints, pipes covered by building elements

Fixture Contamination Backflow and back siphonage

Trap

Trap seal loss Waving out (pressure fluctuation) for short / straight vent, induced siphonage due to absence of trap ventilating pipes; self siphonage of undersized discharge stacks.

Mosquito breeding

Irregular cleaning and poor housekeeping

900