Field Test of Boiler Primary Loop Temperature Controller

Stacey Rothgeb, P. Glanville, P. Rowley, L. Brand, D. Schroeder, Stacey Rothgeb (NREL Technical Monitor)

Research output: NRELSubcontract Report


Beyond these initial system efficiency upgrades are an emerging class of Advanced Load Monitoring (ALM) aftermarket controllers that dynamically respond to the boiler load, with claims of 10% to 30% of fuel savings over a heating season. For hydronic boilers specifically, these devices perform load monitoring, with continuous measurement of supply and in some cases return water temperatures.Energy savings from these ALM controllers are derived from dynamic management of the boiler differential, where a microprocessor with memory of past boiler cycles prevents the boiler from firing for a period of time, to limit cycling losses and inefficient operation during perceived low load conditions. These differ from OTR controllers, which vary boiler setpoint temperatures with ambientconditions while maintaining a fixed differential. PARR installed and monitored the performance of one type of ALM controller, the M2G from Greffen Systems, at multifamily sites in the city of Chicago and its suburb Cary, IL, both with existing OTR control. Results show that energy savings depend on the degree to which boilers are over-sized for their load, represented by cycling rates. Alsosavings vary over the heating season with cycling rates, with greater savings observed in shoulder months. Over the monitoring period, over-sized boilers at one site showed reductions in cycling and energy consumption in line with prior laboratory studies, while less over-sized boilers at another site showed muted savings.
Original languageAmerican English
Number of pages51
StatePublished - 2014

Bibliographical note

Work performed by Partnership for Advanced Residential Retrofit, Des Plaines, Illinois

NREL Publication Number

  • NREL/SR-5500-62342

Other Report Number

  • DOE/GO-102014-4457


  • Building America
  • central heating
  • hydronic boiler
  • load monitoring
  • low-rise multifamily
  • outdoor temperature reset
  • Parr
  • residential
  • residential buildings


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