Water Use in High-Performance Buildings

Summary

The objective of EL’s Net-Zero Energy, High-Performance Buildings research program is to advance measurement science to move the nation toward net-zero energy, high-performance buildings while maintaining a healthy indoor environment. Water heating and premise plumbing systems are key elements of healthy, high-performance buildings since living and thriving in buildings is dependent on efficient delivery of clean, potable water. According to the U.S. Geological Survey, water use in the country is approximately 322 billion gallons per day, (1) and the operation of buildings accounts for nearly 12% of that quantity.(2) Furthermore, the second largest energy expenditure in U.S. buildings is water heating at 19% (1 745 trillion Btu) of total site energy. (3) Therefore, achieving greater water and energy efficiency in buildings continues to be the priority of researchers, builders, and standards and codes organizations.

A series of policy actions including the Safe Drinking Water Act of 1974, Energy Security Act of 1980, Energy Policy Act of 1992 led to notable achievements such as large reductions in energy and water use in buildings, and reduction of lead in plumbing products. However, lower water consumption has had unintended negative consequences for building plumbing systems. Low flows lead to: increased pipe corrosion, deposition of corrosion byproducts, decreased waste conveyance, depletion of disinfectant residuals, lower water temperatures in pipe, increased formation of biofilms, and enhanced environments conducive for pathogen growth. As such, the plumbing industry, including the International Association of Plumbing and Mechanical Officials (IAPMO) and International Code Council (ICC), have called for updating data and tools for redeveloping plumbing codes and design guidelines.

The activities of this project aim to support a better understanding of the connection between reduced water use, efforts to reduce building energy consumption (specifically for heating water), and factors that contribute to water quality concerns to ensure safe and sustainable water heating and plumbing systems in buildings.

Description

Objective:  To develop new measurement methods, tools, and modeling techniques, and collect data to improve building water efficiency, improve water heating energy efficiency standards and codes, and quantify water quality impacts of efficiency measures on high-performance building plumbing systems.

What is the technical idea?  
For many years, NIST has studied building water heating energy efficiency in support of the development of improved test methods for residential and commercial water heaters. However, this project targets a more holistic view of water use in buildings. In past FYs, this project successfully convened stakeholders in the building energy efficiency, water efficiency, and water quality communities at a workshop to gather input on what are the foremost measurement science research needs for improved premise plumbing systems (FY18). Based on the output of that workshop and other efforts to gather information from stakeholders, a detailed report on research needs for premise plumbing systems was published (FY20).

Among the research needs highlighted in this report was the need for accurate and validated models to simulate building plumbing networks. For example, models are needed to better simulate water demand schedules for buildings; understand hydraulic behavior within pipes, fittings, and fixtures; accurately simulate the transport of metals and disinfectants in buildings; and predict temperatures within water heating and plumbing systems. Modeling efforts were started in FY20 and began with simulating a plumbing system in a high-performance residential building (NZERTF) to determine factors such as water age and disinfectant residuals throughout the system that are impacted by its novel design. The next step was to include a temperature model into the simulation to predict heat losses from and heat transfer within hot water pipe. Temperature data taken of the NZERTF plumbing system in field studies were used to validate the thermal simulation.

In FY21, this project will expand current premise plumbing modeling capabilities to better simulate conditions within plumbing networks. Currently, there are few tools that can predict conditions in low-water flow plumbing that can result in disinfectant loss, chemical accumulation, and biofilm growth. Testing of novel heat pump water heaters will continue in the NZERTF in order to better understand their impacts on energy use, including distribution losses.

What is the research plan? 
This project will continue existing efforts to better understand emerging, energy-efficient water heating technologies on the market. First, in conjunction with EL researchers investigating geothermal heat pumps, we will evaluate a ground-source combined appliance for space heating and cooling, and water heating. In FY20, the combined system was installed in the laboratory and instrumented. In FY21, it will be tested under the “ANSI/ASHRAE Standard 206: Method of Test for Rating of Multi-Purpose Heat Pumps for Residential Space Conditioning and Water Heating” to assess whether the method of test adequately measures its heating and cooling capacity and, if not, to determine what revisions to the test are needed . Second, we will continue the performance evaluation of a novel residential water heater that uses a heat pump located outdoors and CO2 as a refrigerant. In FY20, this unit was tested in the laboratory and installed in the NZERTF to initiate a year-long study of its energy performance, starting with the 2020 cooling season. For FY21, the heating season performance analysis will be completed, and a WERB-approved publication will be written that summarizes findings of the 12-month evaluation at the NZERTF and compares the heating capacity to that measured in the laboratory.

The effort to develop accurate and validated plumbing simulations will continue in FY21. Last year, we used the NZERTF PEX-manifold water distribution system as an example to predict the hydraulics, water age, disinfectant residual, and water temperatures throughout a high-performance building using the public domain software, EPANET. In FY21, a simulation will be created for a traditional plumbing layout designed to meet the demand of the NZERTF utilizing existing guidelines for pipe sizing and length. The purpose of this effort is to compare the water temperature and quality performance of water-efficient plumbing designs to more conventional plumbing networks, and to better understand both the advantages and disadvantages of new designs. Additionally, the techniques use to model the water age, disinfectant residual and water temperature within the NZERTF plumbing system will be applied to a plumbing simulation of a non-residential building type (yet to be determined). Because EPANET was developed to model water distribution systems (between water utilities and buildings), the tool has limitations when being used for pipes inside buildings. The work in this project will provide much needed data to improve the use of EPANET for premise plumbing.

In FY21, water- and energy-efficiency and water quality stakeholders will continue to be engaged through this project. Following the successful reception of the “Measurement Science Research Needs for Premise Plumbing Systems” report, we will communicate with stakeholders to discuss and prioritize the research needs to convert them from a list to a roadmap. Organizations, including NIST, can then determine which deliverables align with their goals and objectives and commit resources to accomplishing them. This will take the form of interactive webinar or in-person workshop by the end of the FY.

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[1] Dieter, C.A., Maupin, M.A., Caldwell, R.R., Harris, M.A., Ivahnenko, T.I., Lovelace, J.K., Barber, N.L., and Linsey, K.S., 2018, “Estimated use of water in the United States in 2015: U.S. Geological Survey Circular 1441,” 65 p., https://doi.org/10.3133/cir1441.

[2] U.S. Green Building Council, http://www.usgbc.org/articles/green-building-101-how-does-water-efficie…, 21 May 2014.

[3] U.S. Energy Information Administration, 2018, “Residential Energy Consumption Survey 2015,” https://www.eia.gov/consumption/residential/data/2015/index.php.