Research Project Information

Research Project Summary Information

Field monitoring of solar thermal systems on buildings with domestic hot water recirculation(19712)

Bright Power, Inc.


There is not sufficient, actionable information available on appropriate methods to integrate a solar thermal system into a building with a domestic hot water (DHW) system that includes a recirculation pump and a mixing valve. This represents a critical issue: most multifamily buildings greater than 10 units and commercial buildings with central DHW systems have such a system, which represents thousands of buildings across New York City and State. Bright Power designed and installed a 24 collector solar thermal DHW (SDHW) system at a Bronx multifamily apartment building following ASHRAE Solar Design Manual recommendations. It was quickly observed that the system was providing less benefit than expected. Bright Power conducted a number of in-house studies in an attempt to determine the cause for this occurrence without success. Bright Power concluded a more thorough and detailed analysis is required to establish flow patterns through the SDHW system. Once the flow patterns are documented, design changes could be developed to improve the SDHW system’s performance.

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Project Description

Bright Power, Inc. will install monitoring sensors and data loggers on the Bronx multifamily SDHW system to measure temperatures and flow rates during various operating conditions. The SDHW system will be monitored for three to four months. Bright Power will analyze the collected data to establish the cause for the SDHW system’s low performance. Proposed solutions to mitigate this occurrence will developed.


Cold water bypass has been estimated to reduce the performance of the studied system by 45%. A simple methodology was demonstrated to detect the occurrence of cold water bypass in a building with a DHW recirculation system. The methodology could be used as step in the design process of a solar thermal system to ensure the installed piping minimizes cold water bypass's adverse effect.

Project Results

After ruling out unforeseen interactions between the building’s mixing valve, the recirculation loop and the solar water heating system, Bright Power discovered that after the building water meter, incoming cold water was bypassing the solar storage preheater tanks, the building’s boiler, and the mixing valve, and was entering the hot water recirculation loop at some unknown point. Bright Power estimates that this cold water bypass was reducing the performance of solar water heating system by 45%, effectively doubling its payback period. Bright Power believes a follow-up study with more buildings should be conducted to determine if the observed problem is widespread. Bright Power also believes multifamily buildings with combined heat and power systems should be included in such a follow-up study, since the latter could potentially exhibit the same underperformance as the solar water heating system. An alternate piping design was developed to minimize the adverse effect of cold water bypass at the studied building.


Bright Power, Inc.
11 Hanover Sq Fl 15th
New York, NY 10005

Principle Investigator

Andrew McNamara

Universities Involved


Project Type:

Product Demonstration

Technologies Types:

Building Systems
Solar Thermal (heating & cooling)

NYSERDA Contact Information

Robert Carver


R&D - Buildings Research

Contract Details

Start Date: 11/1/2010
Project Status: Active
Contract Number: 19712

Last Updated: 4/17/2014