Premise Plumbing Systems for High-Performance Buildings

Summary

Premise plumbing systems provide an essential building service, but their design and operation need to be modernized as existing plumbing technology has lagged current performance requirements. Growing awareness of the health and safety impacts of building water quality, along with increasing demands to manage water and energy consumption, have led to the identification of significant knowledge gaps in premise plumbing system design, installation, operation, and maintenance. Current design approaches are primarily based on technical data that were developed in the 1940s and earlier, which assumed higher water flow rates than those currently existing in most buildings and the use of pipe materials and design concepts that have been largely replaced by newer alternatives. Water use in buildings is much lower than assumed in the system design. These lower flow rates increase residence times in plumbing systems, reducing the effectiveness of disinfectant chemicals and, thus, enhancing the potential for growth of opportunistic premise plumbing pathogens (OPPP). Another critical challenge is maintaining water safety while reducing energy and water consumption; for example, conservation measures that have reduced hot water temperatures throughout premise plumbing and water flows through pipe have provided conditions more conducive to the growth of OPPP such as Legionella.

For modern premise plumbing systems to meet the performance goals of protecting occupant health and managing consumption, an entirely new technical knowledge base must be developed. This project aims to provide a better understanding of the connection between water use, building energy consumption (specifically for heating water), and water quality in support of safe water heating and plumbing systems in buildings. FY25 efforts will focus on improving methods to quantify and predict OPPP growth in water heating systems (including performing risk assessments for pathogen exposure to building occupants), further exploring pressure drops associated with a variety of plumbing fittings, and continuing performance measurements on novel water heating technologies.

Description

Objective
To develop new measurement methods, modeling approaches, and data to support improvements in building plumbing design, utility consumption, and water quality. The results of these efforts are intended to support standards development and industry programs to advance innovative technology and improve building design and operation, targeting better performing systems at lower first and operational cost.

Technical Idea  
The technical idea is to advance understanding of water use and water-related energy use in buildings and the impacts on water quality within premise plumbing systems. This project is focused on (1) quantifying chemical and microbial water quality in building hot water systems, and correlating energy- and water-savings measures to indoor water quality; (2) developing measurement science needed to establish standardized and precise means of characterizing pressure loss due to modern plumbing fittings; (3) assessing the performance of advanced water heating technologies; and (4) engaging with industry and other partners to better understand research needs and transfer research results.

To pursue these technical goals, the team is conducting experiments to assess the impact of hot water system operational factors – intended to reduce consumption – on chemical and biological water quality through an automated test apparatus and advanced measurements. In FY23, a test rig with instrumented electric storage water heaters was operated to evaluate water quality parameters under various temperature setpoints and demand conditions. A common industry-recommended energy savings practice is to lower water heater setpoints to 120 F (49 C), which is in the growth temperature range for several opportunistic pathogens. Low water usage can also negatively impact tank water quality because of high water age, decay of disinfectant residual, and lower levels of incoming residual. Thus, water usage patterns need to be studied for their impact on water quality parameters. In FY24, instruments were installed, calibrated, and validated that allow for real-time monitoring of influent and effluent water for parameters such as pH, conductance, turbidity, total organic carbon (TOC), and total/free chlorine. The purpose of these instruments was to determine whether continuous measurements would provide building operators the data needed to predict end-use water quality without having to conduct arduous sampling protocols. In FY24, the team further expanded the test rig to prepare for future evaluation of point-of-use water quality intervention devices. These commercially available devices treat drinking water to reduce OPPPs at the tap and include methods such as filtration, ultraviolet (UV) light disinfection, or reverse osmosis (RO). Understanding the efficacy of intervention devices will provide much-needed data and science-based recommendations for the advancement of current NSF/ANSI standards.  

As plumbing codes are updated and pipe diameters decrease to provide the required flow in a building water system, pressure losses across plumbing components become more significant in design. In past years, the team designed, constructed, and validated a new laboratory facility (the NIST Plumbing Hydraulics Lab (PHL)) to acquire data on pressure-flow relationships for a range of plumbing fittings and components. In the apparatus, pressure losses in modern fittings are measured as a function of various parameters (e.g., flow rate, temperature, and geometry) using an automated pressure distribution measurement system across the test section. During FY24, the researchers validated the apparatus that had a ¾-in diameter test section, collected data on pressure drops across straight pipe and elbow copper fittings, and began evaluating plastic press-to-connect elbows. It was determined that modifications to the test rig were essential to obtain stable and repeatable pressure measurements. The team has begun to reconfigure the rig to accommodate a ½-in diameter test section to ensure laminar flow. 

Additional activities in this project include continuing NIST’s technical characterization of novel water heating systems.  In conjunction with EL researchers investigating geothermal heat pumps, a laboratory evaluation of a ground-source combined appliance for space heating and cooling, and water heating has been initiated using the “ANSI/ASHRAE Standard 206: Method of Test for Rating of Multi-Purpose Heat Pumps for Residential Space Conditioning and Water Heating.” These data will allow standards developers to assess whether the current method of test adequately measures the heating and cooling capacity of ground-source combined appliances and, if not, to determine what revisions to the test are needed.

Research Plan
In FY25, the previous year’s efforts in investigating the microbial ecology of building hot water systems will continue. The second phase of water heater experiments will focus on water quality measurements of two electric storage water heaters (under different operating conditions), and at fixtures downstream of pipe runs included in the expanded test bed. A modular test section will allow for the installation of various point-of-use intervention devices, such as physical filters, and UV and RO devices. FY25 activities will begin with the team adding additional controls and sensors (for temperature and flow) to new parts of the test bed, calibrating sensors, and validation of the updated rig. The team will work with NIST statisticians to develop a Design of Experiment for evaluating water quality treatment devices, given various limitations. We will iteratively amend the design of experiment as we conduct shake-down tests and initial experiments during Q1. The methods required to quantify the target OPPP species in samples we collect from the test lab will also need to be optimized. The team will devote some resources to exploring species-specific culture methods (e.g., plating for Legionella pneumophila) and improving Polymerase Chain Reaction (ddPCR) protocols. This activity will be important in the future for identifying correlations between the measurements that building managers make to monitor plumbing systems and molecular assessments, such as PCR, that although they provide more information on microbial water quality, they also have an associated cost and time burden. Finally, the team will work to develop Quantitative Microbial Risk Assessment (QMRA) models to estimate the risk of infection based on the presence and concentrations of OPPPs in samples collected from the NIST test facility during a prior water quality study there.

The NIST PHL, built and validated in previous years, will undergo further improvements to allow for high-accuracy pressure drop measurements across a range of plumbing components in FY25. With modifications to reduce the diameter of the test section from ¾ in to ½ in (completed this FY), another round of testing will commence to obtain data from straight pipe (copper) and elbows (copper and plastic). A report will be published to disseminate both sets of data. Additionally, the team will work on the design of a new, larger test rig that will be in the NIST plumbing tower and allow for the measurement of pressure drop across fittings up to 1 inch in diameter. In FY25, the team will focus on renovating the top level of the plumbing tower (which will house water tanks for gravity-driven flow through the test apparatus), designing the plumbing layout to the new test section, and developing instrumentation. In tandem with laboratory efforts, the team will continue to participate in the International Code Council (ICC 815) on Sizing Water Distribution, Drainage and Venting Standard Consensus Committee. Activities will eventually inform the draft of a standard test method to measure pressure drops across plumbing fittings and components that will be submitted to an appropriate standards development organization (SDO).

This project will continue the performance evaluation of a ground-source combined appliance for space heating and cooling and water heating. After completion of laboratory tests under controlled conditions – as stipulated under the “ANSI/ASHRAE Standard 206: Method of Test for Rating of Multi-Purpose Heat Pumps for Residential Space Conditioning and Water Heating” – the laboratory test rig will be dismantled and reassembled at our residential test facility.  Under this project, the water use automation for the water heating portion of the system will be implemented for a 12-month test period, and temperature, flow, and energy consumption data will be collected. These data (both from the laboratory and the field-installation) will allow standards developers to assess whether the current method of test adequately measures the heating and cooling capacity of ground-source combined appliances.