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Title: Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment

Abstract

This project analyzed combined condensing water heaters or boilers and hydronic air coils to provide high efficiency domestic hot water (DHW) and forced air space heating. Called 'combi' systems, they provided similar space and water heating performance less expensively than installing two condensing appliances. The system's installed costs were cheaper than installing a condensing furnace and either a condensing tankless or condensing storage water heater. However, combi costs must mature and be reduced before they are competitive with a condensing furnace and power vented water heater (energy factor of 0.60). Better insulation and tighter envelopes are reducing space heating loads for new and existing homes. For many homes, decreased space heating loads make it possible for both space and domestic water heating loads to be provided with a single heating plant. These systems can also eliminate safety issues associated with natural draft appliances through the use of one common sealed combustion vent. The combined space and water heating approach was not a new idea. Past systems have used non-condensing heating plants, which limited their usefulness in climates with high heating loads. Previous laboratory work (Schoenbauer et al. 2012a) showed that proper installation was necessary to achieve condensing with high efficiencymore » appliances. Careful consideration was paid to proper system sizing and minimizing the water temperature returning from the air handling unit to facilitate condensing operation.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Univ. of Minnesota, St. Paul, MN (United States). NorthernSTAR Building America Partnership
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (EE-5B)
OSTI Identifier:
1369136
Report Number(s):
NREL/SR-5500-61313; DOE/GO-102017-4378
DOE Contract Number:
AC36-08GO28308
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; residential; residential buildings; NorthernSTAR; Building America; combi heating systems; forced air combi systems; hydronic air handlers; boiler based combi systems; tankless water heater based combi systems; storage water heater based combi systems; DHW performance; combi system summer efficiency; dual integrated appliances; direct vent burner

Citation Formats

Schoenbauer, Ben, Bohac, Dave, McAlpine, Jake, and Hewett, Martha. Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment. United States: N. p., 2017. Web. doi:10.2172/1369136.
Schoenbauer, Ben, Bohac, Dave, McAlpine, Jake, & Hewett, Martha. Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment. United States. doi:10.2172/1369136.
Schoenbauer, Ben, Bohac, Dave, McAlpine, Jake, and Hewett, Martha. Fri . "Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment". United States. doi:10.2172/1369136. https://www.osti.gov/servlets/purl/1369136.
@article{osti_1369136,
title = {Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment},
author = {Schoenbauer, Ben and Bohac, Dave and McAlpine, Jake and Hewett, Martha},
abstractNote = {This project analyzed combined condensing water heaters or boilers and hydronic air coils to provide high efficiency domestic hot water (DHW) and forced air space heating. Called 'combi' systems, they provided similar space and water heating performance less expensively than installing two condensing appliances. The system's installed costs were cheaper than installing a condensing furnace and either a condensing tankless or condensing storage water heater. However, combi costs must mature and be reduced before they are competitive with a condensing furnace and power vented water heater (energy factor of 0.60). Better insulation and tighter envelopes are reducing space heating loads for new and existing homes. For many homes, decreased space heating loads make it possible for both space and domestic water heating loads to be provided with a single heating plant. These systems can also eliminate safety issues associated with natural draft appliances through the use of one common sealed combustion vent. The combined space and water heating approach was not a new idea. Past systems have used non-condensing heating plants, which limited their usefulness in climates with high heating loads. Previous laboratory work (Schoenbauer et al. 2012a) showed that proper installation was necessary to achieve condensing with high efficiency appliances. Careful consideration was paid to proper system sizing and minimizing the water temperature returning from the air handling unit to facilitate condensing operation.},
doi = {10.2172/1369136},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Jun 23 00:00:00 EDT 2017},
month = {Fri Jun 23 00:00:00 EDT 2017}
}

Technical Report:

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  • This project analyzed combined condensing water heaters or boilers and hydronic air coils to provide high efficiency domestic hot water (DHW) and forced air space heating. Called "combi" systems, they provided similar space and water heating performance less expensively than installing two condensing appliances. The system's installed costs were cheaper than installing a condensing furnace and either a condensing tankless or condensing storage water heater. However, combi costs must mature and be reduced before they are competitive with a condensing furnace and power vented water heater (energy factor of 0.60). Better insulation and tighter envelopes are reducing space heating loadsmore » for new and existing homes. For many homes, decreased space heating loads make it possible for both space and domestic water heating loads to be provided with a single heating plant. These systems can also eliminate safety issues associated with natural draft appliances through the use of one common sealed combustion vent. The combined space and water heating approach was not a new idea. Past systems have used non-condensing heating plants, which limited their usefulness in climates with high heating loads. Previous laboratory work (Schoenbauer et al. 2012a) showed that proper installation was necessary to achieve condensing with high efficiency appliances. Careful consideration was paid to proper system sizing and minimizing the water temperature returning from the air handling unit to facilitate condensing operation.« less
  • Two technologies - SO/sub 2/ scrubber retrofits and the repowering of plants with coal gasification - are options to help utilities meet federal emission standards. Although the superior sulfur removal capability of gasification plants may allow retrofitting of fewer plants and the repowered plants would produce considerable additional electricity, gasification plus repowering is not yet economically competitive with scrubber retrofitting. Researchers performed an engineering design/cost study for a nominal 600-MW high-sulfur coal-fired plant in the Midwest. They examined plant performance as well as capital and operating costs for both SO/sub 2/ scrubber retrofitting and gasification repowering systems. In comparing themore » two methods, they assumed that scrubbing would remove 90% of the SO/sub 2/, compared with 98.5% for gasification repowering. To properly locate the new facilities, the design called for considerable modifications. Critical modifications for SO/sub 2/ scrubber retrofitting included connecting a new flue duct and installing isolation dampers. Plant additions and modifications for the repower case proved far more extensive, and included significant changes to the boiler. Cost estimates showed that the net levelized annual costs of the coal gasification repower option would be almost three times that of the SO/sub 2/ scrubber option. This calculation takes into account the fact that a repowered unit produces about 40% more electricity. Additionally, the potentially superior sulfur removal capability of gasification did not appear to outweigh the high cost of implementation. 17 figs., 22 tabs.« less
  • National programs such as Home Performance with ENERGY STAR® and numerous other utility air-sealing programs have made homeowners aware of the benefits of energy-efficiency retrofits. Yet these programs tend to focus only on the low-hanging fruit: they recommend air sealing the thermal envelope and ductwork where accessible, switching to efficient lighting and low-flow fixtures, and improving the efficiency of mechanical systems (though insufficient funds or lack of knowledge to implement these improvements commonly prevent the implementation of these higher cost upgrades). At the other end of the spectrum, various utilities across the country are encouraging deep energy retrofit programs. Althoughmore » deep energy retrofits typically seek 50% energy savings, they are often quite costly and are most applicable to gut-rehab projects. A significant potential for lowering energy use in existing homes lies between the lowhanging fruit and deep energy retrofit approaches—retrofits that save approximately 30% in energy compared to the pre-retrofit conditions. The energy-efficiency measures need to be nonintrusive so the retrofit projects can be accomplished in occupied homes.« less
  • National programs such as Home Performance with ENERGY STAR® and numerous other utility air sealing programs have brought awareness to homeowners of the benefits of energy efficiency retrofits. Yet, these programs tend to focus on the low-hanging fruit: air-sealing the thermal envelope and ductwork where accessible, switch to efficient lighting, and low-flow fixtures. At the other end of the spectrum, deep-energy retrofit programs are also being encouraged by various utilities across the country. While deep energy retrofits typically seek 50% energy savings, they are often quite costly and most applicable to gut-rehab projects. A significant potential for lowering energy usagemore » in existing homes lies between the low hanging fruit and deep energy retrofit approaches - retrofits that save approximately 30% in energy over the existing conditions. A key is to be non-intrusive with the efficiency measures so the retrofit projects can be accomplished in occupied homes. This cold climate retrofit project involved the design and optimization of a home in Connecticut that sought to improve energy savings by at least 30% (excluding solar PV) over the existing home's performance. This report documents the successful implementation of a cost-effective solution package that achieved performance greater than 30% over the pre-retrofit - what worked, what did not, and what improvements could be made.« less
  • The proposed ASHRAE Standard 152P ''Method of Test for Determining the Design and Seasonal Efficiencies of Residential Thermal Distribution Systems'' (ASHRAE 2002) has recently completed its second public review. As part of the standard development process, this study compares the forced air distribution system ratings provided by the public review draft of Standard 152P to measured field results. 58 field tests were performed on cooling systems in 11 homes in the summers of 1998 and 1999. Seven of these houses had standard attics with insulation on the attic floor and a well-vented attic space. The other four houses had unventedmore » attics where the insulation is placed directly under the roof deck and the attic space is not deliberately vented. Each house was tested under a range of summer weather conditions at each particular site, and in some cases the amount of duct leakage was intentionally varied. The comparison between 152P predicted efficiencies and the measured results includes evaluation of the effects of weather, duct location, thermal conditions, duct leakage, and system capacity. The results showed that the difference between measured delivery effectiveness and that calculated using proposed Standard 152P is about 5 percentage points if weather data, duct leakage and air handler flow are well known. However, the accuracy of the standard is strongly dependent on having good measurements of duct leakage and system airflow. Given that the uncertainty in the measured delivery effectiveness is typically also about 5 percentage points, the Standard 152P results are acceptably close to the measured data.« less