Expert Meeting Report: 

Recommendations for Applying 

Water Heaters in Combination 

Space and Domestic Water 

Heating Systems

A. Rudd, K. Ueno, D. Bergey, R. Osser

Building Science Corporation

June 2012
i 

This report received minimal editorial review at NREL.

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ii

Expert Meeting Report: Recommendations for Applying 

Water Heaters in Combination Space and Domestic Water 

Heating Systems

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by: 

A. Rudd, K. Ueno, D. Bergey, R. Osser

Building Science Corporation 

30 Forest Street

Somerville, MA 02143

NREL Technical Monitor: Cheryn Engebrecht

Prepared Under Subcontract No. KNDJ-0-40337-00 

June 2012 
 

iii

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iv

Contents

Definitions .................................................................................................................................................... v

Executive Summary................................................................................................................................... vi

1 Meeting Topic, Agenda, and Location................................................................................................ 1

2 Introduction ........................................................................................................................................... 2

3 Summary of Discussions ..................................................................................................................... 3

3.1 What are the current industry understandings and experiences relative to the use of 

combination space and domestic water heating systems in general, and in specific related 

to the use of tankless water heaters? ....................................................................................3

3.2 How does cycling frequency and short-cycling affect the efficiency and life of tankless 

water heaters?.......................................................................................................................4

3.3 How important are hot water delivery problems associated with hot/cold plug flow (cold 

water sandwich) and trickle flow? .......................................................................................4

3.4 How much does the addition of a small, insulated, storage tank (that acts as a multiport 

manifold and a buffer against hot water delivery problems) affect overall efficiency, cost, 

and maintenance? .................................................................................................................5

3.5 In order to maximize condensing operation, heating coil water supply temperature should 

be as low as possible, but what are the limits of that to provide comfortable air delivery? 

What are the related issues and recommendations related to hydronic coil sizing and 

increased air handler and circulator runtime? ......................................................................5

3.6 What are the issues and effective solutions related to mineral scale in piping and heat 

exchangers, and clogging of inlet strainers, requiring maintenance? ..................................6

3.7 What are the economic advantages and disadvantages of combination systems versus 

traditional furnace and water heater designs or versus traditional boiler and indirect water 

heater designs? .....................................................................................................................7

4 Summary of Gaps and Barriers........................................................................................................... 9

4.1 What new testing, field studies, and standards work are needed to fill important 

knowledge gaps or barriers that could impede efficient and reliable combination system 

applications? ........................................................................................................................9

5 Next Steps ........................................................................................................................................... 11

Appendix A: Meeting Agenda .................................................................................................................. 12

Appendix B: Attendant List...................................................................................................................... 18

Appendix C: Presentations ...................................................................................................................... 20
 

v 

Definitions

BSC Building Science Corporation

CEE Center for Energy and Environment

Combination System combination space and domestic water heating system

DHW Domestic Hot Water

gpm Gallons per Minute

NRC Natural Resources Canada

SAT Supply Air Temperature

TWH Tankless Water Heater

SWH Storage-Type Water Heater
 

vi 

Executive Summary

The topic of this meeting was “Recommendations for Applying Water Heaters in Combination 

Space and Domestic Water Heating Systems.” Presentations and discussions centered on the 

design, performance, and maintenance of these combination systems, with the goal of developing 

foundational information toward the development of a Building America Measure Guideline on 

this topic. The meeting was held at the Westford Regency Hotel, in Westford, Massachusetts, on 

July 31, 2011. As residential building enclosure improvements continue to drive heating loads 

down, being able to use the same water heating equipment for both space heating and domestic 

water heating (combination systems) becomes very attractive from a cost and space-saving 

perspective. Before committing to wide-scale implementation of such combination space and 

domestic water heating systems for high performance buildings, whether new or retrofit, design 

decisions affecting performance, maintenance, and occupant acceptability need to be well 

understood. Current performance rating procedures for this type of water heating system, and its 

many variants, are inadequate to provide convincing prediction of estimated savings. In order to 

be assured of meeting the Building America savings goals, results of laboratory and field testing 

results are shared to help with verification of energy savings and their installed persistence.

Discussions about this topic were applicable to single- and multifamily residential buildings, 

both new and retrofitted. From a performance point of view, combination systems utilizing 

tankless water heaters are of particular interest because of the high heating capacity and low 

standby losses. However, consistency of supplied water temperature at low flow rates and during 

rapid on/off usage patterns is a concern. Storage-type water heaters reduce or eliminate those 

concerns, but have high standby losses. Adding a small, external, well-insulated storage volume 

to tankless water heater combination systems may provide a high value solution, but that needs 

to be better understood. Tankless water heaters also have more complex designs and water 

heating strategies that can impact efficiency at different flow rates and temperatures. Intricate 

flow measuring and flow controlling components need to be protected from potential damage by 

foreign particles that may be in the water, but those protection filters can require unacceptable 

cleaning intervals. Combination systems generally require heating and storing water at a higher 

temperature than required for domestic hot water only. The higher the temperature of the stored 

water, the greater the potential for mineral scale and galvanic corrosion. All of these factors need 

to be better understood before firm recommendations can be made relative to wide 

implementation of these systems.

Presentations and discussions covered eight key questions ranging from equipment and system 

design strategies, to laboratory and field tested performance, occupancy interactions and hot 

water use profiles, maintenance issues, practical plumbing perspectives, rating standards, and 

gaps and barriers to efficient wide-scale implementation. 

BSC will continue to monitor two combination systems in New York and expects to add another 

site in Pennsylvania soon. By building on past experience, the collected monitoring data, and the 

information generated by this expert meeting, BSC will draft a Measure Guideline for 

implementing combination space and domestic water heating systems in 2011. It is expected that 

this document will continued to be updated and improved as more is learned. 
 

1 

1 Meeting Topic, Agenda, and Location

The topic of this meeting was “Recommendations for Applying Water Heaters in Combination 

Space and Domestic Water Heating Systems.” Presentations and discussions centered on the 

design, performance, and maintenance of these combination systems, with the goal of developing 

foundational information toward the development of a Building America Measure Guideline on 

this topic.

The meeting was held at the Westford Regency Hotel, in Westford, Massachusetts, on July 31, 

2011. The full meeting agenda is provided in Appendix A. 

A list of the meeting attendees along with their contact information is provided in Appendix B. 
 

2 

2 Introduction

As residential building enclosure improvements continue to drive heating loads down, being able 

to use the same water heating equipment for both space heating and domestic water heating 

(combination systems) becomes very attractive from a cost and space-saving perspective. Before 

committing to wide-scale implementation of such combination space and domestic water heating 

systems for high performance buildings, whether new or retrofit, design decisions affecting 

performance, maintenance, and occupant acceptability need to be well understood. 

Current performance rating procedures for this type of water heating system, and its many 

variants, are inadequate to provide convincing predictions of estimated savings. In order to be 

assured of meeting the Building America savings goals, results of laboratory and field testing 

results are shared to help with verification of energy savings and their installed persistence.

Discussions about this topic were applicable to single- and multifamily residential buildings, 

both new and retrofitted. From a performance point of view, combination systems utilizing 

tankless water heaters (TWHs) are of particular interest because of their high heating capacity 

and low standby losses. However, consistency of supplied water temperature at low flow rates 

and during rapid on/off usage patterns is a concern. Storage-type water heaters (SWHs) reduce or 

eliminate those concerns, but have high standby losses. Adding a small, external, well-insulated 

storage volume to TWH combination systems may provide a high value solution, but that needs 

to be better understood. TWHs also have more complex designs and water heating strategies that 

can impact efficiency at different flow rates and temperatures. Intricate flow measuring and flow 

controlling components need to be protected from potential damage by foreign particles that may 

be in the water, but those protection filters can require unacceptable cleaning intervals. 

Combination systems generally require heating and storing water at a higher temperature than 

required for domestic hot water (DHW) only. The higher the temperature of the stored water, the 

greater the potential for mineral scale and galvanic corrosion. All of these factors need to be 

better understood before firm recommendations can be made relative to wide implementation of 

these systems.
 

3 

3 Summary of Discussions

Discussions occurred during and after each of the seven presentations (the presentations are 

provided in Appendix C). A summary of those discussions is given here in the applicable context 

of the key questions established before the meeting. 

3.1 What are the current industry understandings and experiences relative to 

the use of combination space and domestic water heating systems in 

general, and in specific related to the use of tankless water heaters?

Bosch sees condensing combination heating systems as ideal for radiant floor heating 

applications because of the lower temperature water required (98°–120°F), the long cycle times, 

and the simple controls. DHW priority control is not needed in combination systems used for 

radiant floor heating, because it is inherent in the system, considering that the large pressure drop 

from mains pressure to open tap will take most of the flow compared to the pressure developed 

by a 2 gpm circulator. Rinnai and Bosch see DHW priority as necessary for hydronic air handler 

combination systems to avoid delivery of heating supply air below 100°F, and to avoid problems 

with the heating circulator running without a full pipe of water, which can occur if the circulator 

is above the domestic water taps. Rinnai shuts off the heating circulator when an inline flow 

sensor senses less than 1 gpm in that loop. 

Some installers try to avoid installing a mixing valve by keeping the TWH set point temperature 

at 120°F. Rinnai’s testing shows that a mixing valve is necessary to avoid unacceptably large 

upswings and drops in water temperature at a shower when heating is activated and deactivated. 

In a system without a mixing valve, with the TWH set point at 120°F and the shower adjusted to 

105°F, there was a 4°F upswing at the shower when heating was activated and a 6°F drop when 

heating was deactivated. With a pressure balancing mixing valve set at 120°F, the water heater 

set point temperature at 140°F, and the addition of a small inline buffer volume (1.5 in. diameter 

by 12 in. long pipe, or 1.5 cup), there is no significant change in delivered water temperature at a 

105°F shower at the beginning or end of a heating call. Assuming 50 ft of 3⁄4-in. pipe (about 1 

gal) in the piping from the water heater to the shower, the 1.5 cup buffer volume does not change 

the roughly 1 minute wait time to send hot water to the shower from a cold start. The buffer 

device needs to be well insulated to avoid efficiency loss (Rubatex or Armaflex type insulation 

wall thickness at least half the pipe diameter). Supplying 140°F water to the hydronic air handler 

yielded a 118°F supply air temperature (SAT) and about 105°F return water temperature.

Ongoing testing may allow further optimization for condensing efficiency, i.e. moving the TWH 

set point temperature down with the goal of 100°F return water temperature.

A commenter described a resonant frequency type humming noise problem with TWHs. This can 

be a symptom of TWH exhaust air recirculating back to the unit with the incoming combustion 

air. In this case, a cold climate kit (long-nose snout) may be needed to better separate the two air 

streams.

Testing by Steven Winter Associates has indicated that TWH efficiency changes with firing rate 

and water temperatures. Low firing rates seem to result in lower efficiency. Bosch noted that this 

is due to a common TWH approach of feeding a single segmented burner with several gas valves 

to modulate capacity. To keep efficiency high at low firing rates, Bosch modulates capacity by 
 

4 

turning any of four burners either full on or full off. In this way, when any burner is operating, it 

is always operating at full efficiency with the proper air/fuel mix across the entire burner.

However, this approach causes the Bosch units to have a higher minimum firing rate (19 kBtu/h) 

than other units (15 kBtu/h), which means that the heater may not turn on at low flow rates and 

elevated entering water temperature (>70°F). This is especially problematic when trying to use 

solar preheated water, but it can also be a problem in southern climates where the entering water 

main temperature may be 75°F or higher. A commenter noted that he has this problem with a 

TWH in his Houston home. He has found that he has to increase water demand beyond what is 

possible with a low flow showerhead to get the TWH to turn on. He accomplishes this by turning 

on the hot sink faucet while taking a shower. In a solar preheat application, Building Science 

Corporation (BSC0 solved this problem by using a TWH to keep a 6-gal insulated storage tank 

heated to a controlled set point temperature rather than bringing the preheated water through the 

TWH.

Manufacturers have a real health concern about water stagnation in systems where the heating 

circulator does not run for 6 months. A pump cycling timer is needed to avoid that problem. A 

scald prevention mixing valve is a necessary safety component in any DHW system controlled to 

above 120°F.

3.2 How does cycling frequency and short-cycling affect the efficiency and life 

of tankless water heaters?

Short cycling can lead to customer dissatisfaction and premature failure of component parts.

Bosch defined short cycling as run times shorter than 10 seconds. Many DHW draws are for less 

than 10 seconds, and it is questionable whether any usable energy is delivered in that case. No 

equipment rating standards require testing for that. For combination systems with TWHs, field 

data taken by BSC have shown a 10 times greater cycling rate for a system without a small (12-

gal) storage tank compared to a system with it. It is obvious that equipment life would be 

significantly impacted by such a large difference in on/off cycling of moving parts, but any 

quantification of that is not widely known. 

With little storage and many short DHW draws, much of the TWH system’s electricity

consumption can be for pre- and post-purge operation. 

3.3 How important are hot water delivery problems associated with hot/cold 

plug flow (cold water sandwich) and trickle flow?

When THWs were first introduced in the United States, the water flow rate threshold for heater 

activation was about 0.7 gpm or higher. The industry quickly raised concerns about the 

unavailability of hot water at commonly lower flow rates. Manufacturers have been responding 

to those concerns by lowering the activation threshold, which is now as low as 0.4 gpm, and 

some units can continue to operate as low as 0.26 gpm after it has already been activated at the 

higher threshold. This has significantly reduced the extent of low flow issues.

Bosch and Rinnai acknowledge problems associated with maintaining consistent hot water 

supply temperature with TWHs because of hot/cold plug flow and trickle flow (less than 

activation flow). Both recommend designs that include additional stored water volume to 

overcome that. Bosch described an unpowered (passive) tank and a powered (active) tank option. 
 

5 

The powered tank option is the most robust in solving the problem but requires more energy. The 

unpowered option increases hot water delivery time due to the larger volume of cooled-off water 

when there has not been DHW or heating demand for some time. 

High capacity storage-type water heaters (SWHs) used in combination systems eliminate the 

cold water sandwich and trickle flow problems associated with TWHs, but high jacket heat loss 

and long runtimes to condensing operation reduce efficiency. A condensing SWH starts 

condensing after about 10 to 15 minutes of operation; a condensing TWH starts condensing 

operation almost immediately because cool incoming water cools the combustion exhaust. 

3.4 How much does the addition of a small, insulated, storage tank (that acts as 

a multiport manifold and a buffer against hot water delivery problems) affect 

overall efficiency, cost, and maintenance?

BSC is in the early stages of collecting adequate field data to understand the question of 

efficiency for a system with a 12-gal insulated electric water tank as the storage volume. The 

additional cost of an off-the-shelf 6- to 12-gal insulated electric water heater storage tank is 

about $200. If a bronze or stainless steel circulator is used to circulate water through the TWH, 

that would add $300 to $400. 

The Center for Energy and Environment (CEE) has been conducting laboratory testing that 

shows that the efficiency deficit is large for at least one TWH product with a small, 

underinsulated integral storage/buffer tank.

Rinnai has recently worked out a design recommendation for adding a small, field-installed 

storage volume, but its effect on efficiency has not been evaluated and would depend largely on 

how well the storage volume was insulated.

The A.O. Smith 100 kBtu/h Vertex product with condensing heat exchanger, direct-vent (twopipe sealed combustion), and 50-gal glass-lined tank is probably the best-known overall 

competitor (based on capability and cost) to a combination system with TWH and a small 

storage volume.

Insulating all piping and storage components of any water heating system is vitally important. 

Otherwise, large inefficiency from heat loss will result. One TWH combination system that CEE 

tested had a 2-gal internal storage tank, but it and other piping components were so poorly 

insulated that it had about the same idle heat loss (400 Btu/h, costing about $40/yr) as other 50-

gal SWHs (tank) tested.

3.5 In order to maximize condensing operation, heating coil water supply 

temperature should be as low as possible, but what are the limits of that to 

provide comfortable air delivery? What are the related issues and 

recommendations related to hydronic coil sizing and increased air handler 

and circulator runtime?

A Rinnai chart indicated that condensing TWH efficiency increases from about 87% at 130°F 

return water temperature to about 94% at 80°F return water temperature. To maximize 

condensing operation, pump flow controls can be employed to control return water temperature. 

In other words, if the return water temperature is too high to achieve efficient condensing 
 

6 

operation, the pump flow could be automatically reduced. But that forces a tradeoff with heating 

SAT, because as the pump flow and the return water temperature drops, so does the SAT and the 

hydronic air handler efficiency. Air source heat pumps often operate at SATs below 100°F,

geothermal heat pumps often operate at SATs around 105°F, and whole-house air circulation 

strategies effectively move room temperature air, so the SAT problem can be managed, but 

proper duct design and appropriate supply grille design and placement are critical to avoid cool 

air complaints.

Larger hydronic coils can also be used to lower return water temperature without reducing pump 

flow or air handler efficiency, but that has an economic tradeoff of higher equipment cost. CEE 

testing indicates that hydronic air handler coil sizes need to be much larger to achieve low 

enough return water temperature to provide consistently high condensing efficiency. CEE data, 

averaged for a group of combination systems with condensing water heaters, showed that total 

heating plant efficiency (gas and electric) was about 82% with 120°F return water temperature 

and about 91% with 80°F return water temperature.

A comprehensive control strategy needs to be developed and tested to optimize the control of 

heating pump flow, air handler flow, and TWH heating output, to control on heating water return 

temperature, heating SAT, and DHW supply temperature to better optimize and monitor 

efficiency and comfort of specific combination systems. This would require using expensive 

variable-speed components and additional temperature and flow sensors. 

3.6 What are the issues and effective solutions related to mineral scale in piping 

and heat exchangers, and clogging of inlet strainers, requiring 

maintenance?

Traditionally, TWHs have been mostly used in open systems for DHW only. Any time you cause 

any type of closed system recirculation, such as when water is circulated to keep hot water more 

quickly available at the taps, or such as when water is circulated for space heating, anything 

generated inside the system (e.g., anode rod decay or mineral precipitate), will clog the inlet 

strainer that is designed to protect flow measuring and flow controlling components. In BSC’s 

field experience, the inlet strainer cleaning interval can range from days to months without a 

large pre-strainer, and extended to annual service with a large pre-strainer. The pre-strainer used 

in BSC projects has a 200 micron stainless steel screen, compared to the 238-micron screen in 

the Rinnai TWH’s inlet strainer. Bosch uses a 300-micron inlet strainer.

Rinnai TWHs use a heating method sometimes called flash heating. That control strategy sends 

only a portion of the total water flowing through the unit through the heat exchanger; the rest is 

bypassed and remixed at the unit outlet. The portion going through the heat exchanger is heated 

to 150°–185°F. This is done to prevent condensation and corrosion in a noncondensing heat 

exchanger when the water is being heated to less than 120°F. The lower the requested set point 

temperature, the more the water overheats. Generally the heat exchanger temperature should be 

at least 125°F to avoid condensation. A set point temperature of 140°F is a sweet spot for the 

Rinnai system efficiency and delivered temperature consistency.

It is known that the hotter the water, the more mineral precipitate (mainly calcium carbonate) 

will drop out of solution. This will contribute to scale formation, and BSC’s field experience 
 

7 

indicates that it contributes to clogging of the water heater’s inlet strainer screen whenever 

recirculation is active. 

Navien is a TWH manufacturer that does not use the flash heating method. Navien uses a 

stainless steel heat exchanger and essentially all of the water flowing through the unit flows 

through the heat exchanger where it is heated only as much as needed. This may be an important 

factor in extending inlet strainer cleaning intervals. Future research should explore this in more 

detail.

Bosch believes that the inlet strainer on its equipment can be removed after the first week or so 

of operation after installation or after any new plumbing is done. The basis for this is that, in its 

experience, the potentially damaging foreign materials in the system are generally bits of copper, 

thread tape, and thread sealant from the piping installation, and after those materials are captured 

and removed, the strainer is no longer needed. Perhaps other manufacturers are being too 

conservative with either the micron size of the inlet strainer, or in requiring the continued use of 

the strainer at all. If that is so, perhaps the only problem that BSC has experienced with these 

combination systems to date, that of clogged inlet strainers, could be easily resolved. Although a 

smaller Y strainer may be adequate in some cases, BSC has resorted to adding a large-capacity, 

stainless steel strainer ahead of the TWH filter screen. However, this adds about $150 material 

cost, another 1⁄3 gal of storage to the system, and another fixture to insulate. 

It is unlikely that a combination system would increase scale risk over that of a TWH system 

alone, but because of the recirculation involved, BSC has found inlet filter clogging to be a 

serious problem that must be addressed upfront in the design. 

BSC found that a Clearwave electronic water conditioner can remove calcium carbonate scale in 

piping and prevent new scale from forming. Rinnai TWHs sense when scale is affecting 

efficiency by more than 5% and display a fault condition if this occurs. The Rinnai 

noncondensing TWH combination system where BSC applied the electronic water conditioner 

has gone through four years without a scale fault condition. Excess scale can cause a condensing 

TWH to be noncondensing.

Especially with the higher water temperature common with combination systems, it is important 

to use plastic-lined galvanized nipples for connecting to a steel tank. Unlined nipples will scale 

quickly, reducing and sometimes blocking water flow. Scale can also break loose and contribute 

to clogging the TWH inlet strainer. In an attempt to deal with problematic hard water issues, 

some people oversoften the water, which removes a useful thin protective layer of scale 

formation in copper pipes and hastens thinning of the relatively soft metal by water erosion. Hot 

water recirculation systems also wear out copper pipes and TWHs. It is far better to use good 

piping design and pipe insulation to reduce hot water delivery wait times. 

3.7 What are the economic advantages and disadvantages of combination 

systems versus traditional furnace and water heater designs or versus 

traditional boiler and indirect water heater designs?

Contractor-installed cost for a New York State Energy Research and Development Authority 

combination system retrofit project was $3,500 per system for two identical systems in a twofamily house. Installed combination systems using a condensing TWH, with or without a small 
 

8 

external insulated storage volume, can cost less than half traditional boiler and indirect water 

heater designs. The cost differential is less when comparing combination systems to traditional 

furnace and water heater designs, but it is still in the favor of combination systems as long as the 

water heating efficiency is comparable for both. 

Contractor bids for the CEE project, for a group of four different installed combination systems, 

by two different contractors, showed that costs varied from about $6,000 to $10,000 per system. 

Based on studies done by Natural Resources Canada, a condensing TWH must be used for a 

combination system to achieve the same or better overall efficiency compared to a condensing 

furnace and a 0.62 energy factor water heater in cold climates.

Estimates of system cost comparisons show:

• Lowest cost category: hydronic air handler + condensing SWH and hydronic air handler 

+ condensing TWH

• Middle cost category: condensing furnace and condensing water heater 

• Highest cost category: hydronic air handler + condensing boiler and hydronic air handler 

+ solar preheat. 

A commenter questioned whether combination systems will save energy and capital cost. If the 

systems are not bulletproof, there should be a hesitation to recommend overall, because failures 

can leave long scars. Another commenter felt it was difficult to justify investment on a cost basis 

for condensing water heating. According to a Rinnai tradesman trainer, the lower cost for venting 

a condensing unit cancels the higher cost of the condensing heater. Another commenter 

questioned whether BSC’s general stance on the importance of sealed combustion was a real 

driver yet in the United States, or whether forced draft was adequate. 

Combination systems may make the most economic sense in new construction, because there 

will be only one gas line and vent pipe, there will be no old scaled pipes involved to cause flow 

or inlet filter clogging problems, and proper design of the total system is possible (including 

properly sized and insulated plumbing to avoid extended delay time in delivering water). In 

retrofit cases, the existing gas service line (either the outside utility line or in building) may not 

have adequate capacity to serve the high demand of a TWH or high capacity SWH. 
 

9 

4 Summary of Gaps and Barriers

Discussions occurred during and after each of the seven presentations. A summary of the gaps 

and barriers discussed is given here in the context of the last key question established before the 

meeting. 

4.1 What new testing, field studies, and standards work are needed to fill 

important knowledge gaps or barriers that could impede efficient and 

reliable combination system applications?

New factory-supplied total systems are needed to overcome mixed supplier conflicts. Improved 

design and control methodologies are needed to maximize combination system benefits. This 

includes predicting and achieving better consumer comfort and energy savings. For example, by 

providing stable water temperature throughout the range of common flow rates and use patterns, 

ensuring consistent condensing operation, fully understanding the pros and cons of adding small 

storage volumes to combination systems using TWHs, and adding solar preheat to combination 

systems. 

Building America supported field and laboratory testing is needed to help move that evolution 

along faster. Building America prototype and community homes are ideal for combination 

system applications, because the heating loads are low and the homes maintain temperature for a 

long time, allowing DHW priority control schemes to work well and be unnoticed by the 

occupants. The savings in equipment cost can be applied to other energy efficiency 

improvements, or just make the house or retrofit project more affordable.

To optimize and monitor efficiency and comfort of combination systems, a comprehensive 

control strategy needs to be developed and tested to coordinate the control of the heating 

circulator flow, air handler flow, and TWH heating output. Control parameters would be the 

heating water return temperature (to optimize water heating condensing efficiency), heating SAT

(to optimize space heating efficiency and comfort), and DHW supply temperature after the 

mixing valve (to optimize comfort and safety). This would require a variable-speed space heating 

circulator and fan, modulating or staged gas valve components, and multiple temperature and 

flow sensors. 

There are really no standards or peer-reviewed guides for efficient combination system design. 

Most systems are designed and installed by trial-and-error “experts” from smaller independent 

heating system companies.

In North America two test methods are available for evaluating the performance of combination 

systems. American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard 

124 – 2007, “Methods of Testing for Rating Combination Space-Heating and Water-Heating 

Appliances,” covers gas, oil, and electricity for forced air and hydronic systems, yielding a 

combined annual efficiency. Canadian Standards Association Standard P.9–2011 is under 

development and covers gas and oil, for forced air only, yielding a thermal performance factor, a 

composite space heating efficiency, a water heating performance factor, and a 1-h water delivery 

rating. 
 

10 

The American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard 124 is 

deficient in a number of ways. For example, it allows for testing the components individually, 

but not as a complete operating system, so the real combined performance cannot be assessed. 

Manufacturer controls that may enhance the equipment performance have to be disabled for 

testing. The test method also requires prescribed temperatures and factors that may not provide a 

realistic rating for actual use conditions.

The Canadian Standards Association Standard P.9-2011 is being developed to improve on those 

deficiencies by allowing for customized temperature set points and controls to test the system at 

the conditions in which it operates. It also calls for testing at two weighted part-load conditions 

(15% and 40%), as well as at the maximum input rate in heating mode. 

The rating performance standards for combination systems need to be expanded and improved to 

encompass the new equipment and designs on approaching the market. That is also needed to 

better predict actual performance by testing and modeling more realistic use patterns and a wider 

range of inlet and outlet water temperatures, including for solar preheat to combination systems. 

Manufacturers see benefits in Building America developing third-party programs to determine 

the benefits and application differences between the various technologies, such as the impact on 

water use, electricity and gas consumption and demand, and consumer behavior, then providing 

industry with guidance on best practices. 
 

11 

5 Next Steps

Data should continue to be sought to learn more about actual hot water use profiles for 

combination systems and the response and efficiency of different configurations used to meet 

those demands. BSC will continue to monitor two combination systems in New York and 

expects to add another site in Pennsylvania soon. By building on past experience, the collected 

monitoring data, and the information generated by this expert meeting, BSC will draft a Measure 

Guideline for implementing combination space and DHW systems in 2011. It is expected that 

this document will continue to be updated and improved as more is learned. 

Sharing the knowledge and data we have gained with those involved in Standards activities (test 

methods and performance rating) will produce better information that can be used for predicting 

the performance of installed combination systems, leading to better designs and further savings. 

As always, public standards should be developed with as much technical accuracy as possible 

without stifling private innovation. Continued collaboration with industry partners should 

include sharing field data and operational observations, helping them focus their creative 

investments for the best good.
 

12 

Appendix A: Meeting Agenda
                 

  

 

WWW.BUILDINGAMERICA.GOV 

Agenda for 

Building America Expert Meeting 

on 

Recommendations For Applying Water Heaters In Combination Space 

And Domestic Water Heating Systems 

Date/Time: Sunday, July 31, 2011 

9 am to 3:30 pm 

Location: Westford Regency Hotel 

219 Littleton Road Westford, MA 01886 

P: 800.543.780, 978.692.8200 

Meeting Manager: Armin Rudd, Building Science Corp., P: 717.867.0123 

List of Presenters: 

 Hugh Magande (Rinnai USA) 

The Anatomy of Combination Water and Space Heating Systems 

 Dave Hammond (A.O. Smith) 

Balancing Performance with Customer Expectations 

 David Corbin (Bosch Thermotechnology) 

Combination Space Heating Systems - Addressing the Key 

Questions From a Manufacturers' Perspective 

 Ben Schoenbauer (MN Center for Energy and Environment) 

Installing Combination Systems: Optimized Designs and 

Potential Performance Problems 

 Martin Thomas (Natural Resources Canada) 

Progress On Improved Test and Rating Standards for 

Combination Space and Domestic Water Heating Systems 

 Larry Weingarten 

The Science of Water Heating From a Plumber's Perspective 

 Armin Rudd (BSC) 

Preliminary Field Testing of Combi Systems Using a Tankless 

Water Heater, With and Without a Small Storage Tank 

The objective of this session is to explore the development needs and 

commercial possibilities for wide-scale implementation of improved 

combination space and domestic water heating systems for high performance 

buildings. As enclosure improvements continue to drive heating loads down, 

using the same water heating equipment for both space heating and 

domestic water heating (combi systems) becomes very attractive. However, 

fully understanding this topic is important to verify energy savings (and their 

Building Science Corp, 30 Forest Street, Somerville, MA 02143

978.589.5100 www.buildingscience.com

13
                 

  

 

 

persistence) toward the Building America energy savings goals of 50% by 

2014 to 2017. Discussions on this topic will be applicable to single- and 

multi-family residential buildings, both new and retrofitted. Systems of 

particular interest will include those that use sealed combustion, direct vent 

tankless heaters, condensing or non-condensing, and with or without a 

buffer/manifold tank. Efficiency, performance, cost, and long-term operating 

and maintenance issues will be examined. 

Key questions regarding this meeting: 

1. What are the current industry understandings and experiences relative to 

the use of combination space and domestic water heating systems in 

general, and in specific related to the use of tankless water heaters? 

2. How does cycling frequency and short-cycling affect the efficiency and life 

of tankless water heaters? 

3. How important are hot water delivery problems associated with hot/cold 

plug flow (cold water sandwich) and trickle flow? 

4. How much does the addition of a small, insulated, storage tank (that acts 

as a multiport manifold and a buffer against hot water delivery problems) 

affect overall efficiency, cost, and maintenance? 

5. In order to maximize condensing operation, heating coil water supply 

temperature should be as low as possible, but what are the limits of that to 

provide comfortable air delivery? What are the related issues and 

recommendations related to hydronic coil sizing and increased air handler 

and circulator runtime? 

6. What are the issues and effective solutions related to mineral scale in 

piping and heat exchangers, and clogging of inlet strainers, requiring 

maintenance? 

7. What are the economic advantages and disadvantages of combi systems 

versus traditional furnace and water heater designs or versus traditional 

boiler and indirect water heater designs? 

8. What new testing, field studies and standards work is needed to fill 

important knowledge gaps or barriers that could impede efficient and reliable 

combi system applications? 

Expected Results: 

As a result of this meeting, a summary report will be prepared and peerreviewed before final submission and web posting. It is expected that the 

information obtained, relative to the Key Questions listed above, will lend 

itself toward the eventual production of a guide for the best practice 

Building Science Corp, 30 Forest Street, Somerville, MA 02143

978.589.5100 www.buildingscience.com

14
                 

  

 

 

application of combination space and domestic water heating systems for 

new and retrofit residential construction. 

Invitees: 

Participants will be key people working in the fields of: water heating, space 

heating, new and retrofit residential construction, and building energy 

efficiency. A blend of industry, research, and government participants will be 

sought. 

Meeting Agenda: 

 9 am Welcome and Meeting Introduction 

 Brief Building America Program Overview 

 9:15 to 12:15 Presentations with Q&A time 

o four 30 minute presentations with 10 min Q&A 

o one 15 minute break 

 12:15 to 1:00 Lunch break (lunches provided) 

 1:00 to 2:30 Presentation with Q&A
 

o three 20 minute presentations with 10 min Q&A 

 Group discussion to cover key questions 

 Wrap up, action items, and follow-up plan
 

 3:30 pm Adjourn meeting 

Building Science Corp, 30 Forest Street, Somerville, MA 02143

978.589.5100 www.buildingscience.com

15
                 

  

   

 

 

   

Presenter Bios
 

Hugh Magande 

Hugh Magande is currently Senior Project Engineer and R&D lead at Rinnai 

Corporation. He is a member of supervisory staff with full responsibility for strategic 

planning and leadership of all engineering functions and is currently spearheading 

Rinnai's Energy Policy Programs. Hugh serves as the designated contributor to the 

AHRI-chaired Working Group to address the proposed DOE Test Procedure for 

Residential Water Heaters. Hugh is the primary author of installation and training 

manuals for the Rinnai Hydronic Furnace, and co-author of a textbook titled, 

"Introduction to Thermo‐Fluids Systems Design." Mr. Magande previously worked at 

Carrier Corporation/UTC as a Product Development Engineer, and at 

Steinharter‐Schwarz Associates as an HVACR Designer/Project Coordinator. 

David Hammond 

David is currently the General Manager for A. O. Smith WPC Canada located in 

Fergus, Ontario, Canada. This role has the P&L responsibility for Canada and overall 

management of the manufacturing facilities, operations, sales, marketing and 

engineering departments for the Canadian market. David has been with A.O. Smith 

for 8 years. Previous to A.O. Smith, David had previous positions with Reliance Home 

Comfort, one of Canada’s largest rental companies with over 1.2 million rental water 

heaters in their portfolio. Prior to Reliance Home Comfort, David spent 20 years with 

Union Gas, an Ontario natural gas utility, primarily with Operation and Technical 

responsibilities. 

With over 30 years of industry experience; from a manufacturer to having water 

heater asset performance responsibility to meeting customer’s performance 

expectations; David brings a unique perspective to the water heater industry. 

Southern Ontario has a high market percentage of air handlers in the condo and 

townhouse market having been introduced and supported through natural gas utility 

programs since the early 1990’s. 

David Corbin 

David is a product manager for Bosch Thermotechnology managing gas and electric 

water heating, storage tank, and solar thermal system product lines. He has worked 

in energy efficient water heating since 2006. During this time he has worked in a 

product development role on various products including tankless water heaters, 

condensing boilers, and hydronic air handlers; including applications related design 

work. David has an MBA from Georgia State University and a B.S. in Chemical 

Engineering from Rose-Hulman Institute of Technology 

Ben Schoenbauer 

Ben Schoenbauer is a research engineer at the Center for Energy and Environment in 

Minneapolis, MN. At CEE, Ben has been conducting energy efficiency research for 

both commercial and residential buildings for the last 4 years. He has a Master's 

degree in Mechanical Engineering from the University of Minnesota and a Bachelor's 

degree in Physics from St. John's University. 

Building Science Corp, 30 Forest Street, Somerville, MA 02143

978.589.5100 www.buildingscience.com

16
                 

  

 

Martin Thomas, MSc. , C.Eng. , P.Eng. 

Martin is a Member of ASHRAE and a Professional Engineer. Martin is the Chair of 

ASHRAE SPC 124 (Method of Test for Combination Systems) and the Secretary of 

ASHRAE SPC 118.2 (Method of Test for Residential water Heaters). Martin is a 

Chartered Engineer in the UK and a Professional Engineer in Ontario, Canada. 

Martin has worked for both British Gas R&D and The Canadian Gas Research 

Institute (CGRI). With 25 years of experience, he now works as a Project Engineer 

at CanmetENERGY in Ottawa, which is a part of Natural Resources Canada (i.e. the 

Government of Canada). In his duties, Martin develops, tests, and evaluates new 

residential/commercial technologies that may lead to reduced fuel consumption and 

GHG (or other pollutant) emissions. His work focuses on maximizing efficiency, using 

renewable energy and technology integration. Martin also provides technology 

support to the Office of Energy Efficiency and contributes to the development of 

Canadian and US performance Standards relating to a variety to energy-using 

technologies including combination space / water heating systems. 

Larry Weingarten 

Larry has been involved in hot water and energy related work since 1978. Larry has 

developed a variety of tools and methods for maintaining water heaters and has coauthored a book on the topic. He has also co-authored articles on hot water, energy, 

and plumbing, and conducts workshops on these subjects. Near Monterey California, 

Larry lives in a highly-efficient off-grid solar home he designed and built whose 

radiantly-heated wall systems and daylighting fenestration techniques represent the 

state of the art in near-zero energy homes. 

Armin Rudd 

Armin Rudd is a Principal at Building Science Corporation where he joined in 1999. 

For 12 years prior to that, he worked at the Florida Solar Energy Center, a research 

institute of the University of Central Florida. Armin has 25 years in the field of 

buildings research and consulting with a wide range of experience in residential and 

commercial buildings. His career has been especially focused on space conditioning 

systems, ventilation, dehumidification, and product development. He has authored 

many technical publications and articles; he is a regular presenter at national 

conferences, and has earned 12 U.S. patents. 

Building Science Corp, 30 Forest Street, Somerville, MA 02143

978.589.5100 www.buildingscience.com

17
 

18 

Appendix B: Attendant List
5

10

15

20

25

30

35

Attendance list Combi system expert meeting in Westford, 7/31/2001 

Last Name First Name Company email 

1 Aldrich Robb Steven Winter Associates raldrich@swinter.com 

2 Austin Mike J. Pinnelli Co. mike@pinnelli.com 

3 Bergey Daniel BSC daniel@buildingscience.com 

4 Bianchi Marcus NREL marcus.bianchi@nrel.gov 

Brennan Terry Camroden Associates terry@camroden.com 

6 Chandler Michael Chandler Design-Build michael@chandlerdesignbuild.com 

7 Chitwood Rick Chitwood Energy rick@chitwoodenergy.com 

8 Confrey John Bosch Thermotechnology john.confrey@us.bosch.com 

9 Corbin David Bosch Thermotechnology david.corbin@us.bosch.com 

Glanville Paul Gas Technology Institute paul.glanville@gastechnology.org 

11 McAlpine Jake Sustainable Resource Center j.mcalpine@src.org 

12 Grisolia Anthony IBACOS agrisolia@ibacos.com 

13 Hammond Dave A.O. Smith dhammond@hotwater.com 

14 Healy Gavin Balance Point Home Performanc gavin@balancepointhp.com 

Holladay Martin GBA martin@greenbuildingadvisor.com 

16 Henderson Hugh CDH Energy hugh@cdhenergy.com 

17 Huelman Pat University of Minnesota phuelman@umn.edu 

18 Kenney Gary Affiliated International Managem gary@aim4sustainability.com 

19 Kwak Ted Navien America tedk@navienamerica.com 

Magande Hugh Rinnai US hmagande@rinnai.us 

21 Marcelino Ron Rheem Manufacturing ron.marcelino@rheem.com 

22 McKenna Jim U.S. Boiler Co. jmckenna@usboiler.net 

23 Moore Ray J. Pinnelli Co. ray@pinnelli.com 

24 Oberg Brad IBACOS boberg@ibacos.com 

Osser Roselin BSC rosie@buildingscience.com 

26 Pedrick Greg NYSERDA gap@nyserda.org 

27 Perunko Dan Balance Point Home Performanc balancepoint@hughes.net 

28 Prahl Duncan IBACOS dprahl@ibacos.com 

29 Rogers Michael Green Homes America mike.rogers@greenhomesamerica.com 

Rudd Armin BSC arudd@buildingscience.com 

31 Schoenbauer Ben MN Center for Energy and Enviro bschoenbauer@mncee.org 

32 Thomas Martin NRCan martin.thomas@nrcan.gc.ca 

33 Townsend Brad Masco Contractor Services brad.townsend@mascocs.com 

34 Ueno Kohta BSC kohta@buildingscience.com 

Vieira Rob FSEC robin@fsec.ucf.edu 

36 Watson Richard SSHC, Inc. rwatson@sshcinc.com 

37 Weingarten Larry eleent@mbay.net 

38 Werling Eric US DOE eric.werling@ee.doe.gov 

39 Wigington Linda Affordable Comfort lwigington@affordablecomfort.org 

19
 

20 

Appendix C: Presentations 
7/31/2011
 

Topics of Discussion 

 Tankless technology overview 

 Tankless Heating System: the general idea 

 Temperature Profiles (cold water sandwich issue) 

 No Mixing Valve; No Manifold 

 Mixing Valve; No Manifold 

 No Mixing Valve; w/Manifold 

 w/Mixing Valve and Manifold 

 Condensing Technology 

 Factors Influencing Effectiveness of Condensing Technology 

U.S. average Ground Water temperatures 

EXAMPLE: 

Rinnai Tankless Water Heater’s temperature at controller = 120° 

Subtract the incoming temperature from the water heater’s set 

temperature for ∆T: 120° - 57° = 63° ∆T 

Maximum Flow Rate by Model 

11.0 Using the previous R98LSi/e example of 63°F ∆T, each model will produce: 10.0 

9.0 R94LSi/e R98- 6.3 gpm

R94- 5.1 gpm 8.0 R75LSi/e R75- 4.8 gpm

V53i- 4.0 gpm 7.0 V53e- 3.2 gpm 

6.0 V53i 

5.0 V53e 

4.0 

3.0 

2.0 

1.0 

0.0
 

0 25 50 63 75 100
 125 

T – Temperature Rise (°F) 

Hot Water Flow Rate (gpm) 

Incoming Air 

Heat Exchanger 

Temp.Thermistor 

FR 2 

SV4 

SV2 

Combustion Fan 

Modulating 

Gas Valve/POV 

Bypass 

Out going
 

Temperature
 

Thermistor
 

Tankless Heating Systems 

The Anatomy of Combination Water and 

Space Heating Systems 

Presenter: Hugh Magande, MSEM, MBA, BEME 

Sequence of Operation (Indoor LS-VB Unit) 

1. Water flow begins Exhaust • Water flow sensor sends pulses to the PCB 

•	 When flow exceeds approximately *0.4 gpm the ignition sequence begins. 

*Model dependent 

2. Ignition Sequence 

• Combustion fan turns to allow correct air flow thru unit 

• Spark igniter begins sparking and gas control valve opens to low fire rate 

• When flame rods prove ignition spark igniter stops sparking 

Igniter 

FR 1 3. Normal Operation 

• PCB monitors flame rods, fan motor frequency, flame characteristic, outlet water Burner 

Sensor temperature, temperature set point, and water flow rate SV3 • Gas valve assembly & fan speed modulate gas and air input to meet user demand 

• If demand is very small, only SV1 will allow gas to burner, FR1 will monitor this 

SV1 minimum fire state 

• If demand is large flame can develop across the entire burner 

• Water is heated as it passes thru heat exchanger multiple times 

•	 Heat exchanger strategically overheats water while the fixed or variable bypass 

cools to the set point temperature to provide higher flow rates 

• Water flow control valve is adjusted, as needed 

4. Shut-down Sequence PCB 

• PCB senses flow rate 0.3 gpm or lower 

SV0 or SV Main • Gas control valve closes & water flow control valve resets to standby position 

Water flow • Combustion fan runs for a short period of time at low speed control valve Water Flow 

Sensor 5. Standby Mode 

•	 PCB monitors all components. Freeze protection is 

activated as needed 

If incoming water is 57° and 

requested temperature is 120°, 

∆T is 63° and gpm flow rate is 

5.1 gpm 

63

Understanding Maximum Flow Rate (R94 Lse 

Flow Curve) 

The tankless water heater’s first priority is to provide the set point 

temperature to the user. Based on the ∆T, the tankless product 

may regulate flow to ensure it can provide the selected 

temperature. 

1 

21
 

 

 

 

 

 

 

 

 

 

7/31/2011
 

Tankless Heating System Overview 

Added load; increased Delta T(HWR); Pump start pressure differential 

TWH Set Temperature: 120 F / Sh @ 105 F / Mix @ 110 F 

Sequence: Shower on / AHU on / AHU off 

144 Sec. 4 F up 

swing 

108 Sec. 6 F dn 

swing 

TWH Set Temperature: 120 F / Sh @ 105 F / Mix @ 110 F 

Sequence: Shower on / AHU on 

96 Sec. 4 F up 

swing 

TWH Set Temperature: 120 F / Shower @ 105 F / Mix @ 110 F 

Sequence: Shower on / AHU on 

72 Sec. 7 F dn 

swing 

TWH Set Temperature: 140 F / Shower @ 105 F / Mix @ 110 F 

Sequence: AHU on / Shower on / AHU off 

44 Sec. 3 F dn 

swing 

TWH Set Temperature: 140 F / Shower @ 105 F / Mix @ 120 F 

Sequence: Shower on / AHU on / AHU off 

Flat 72 Sec. 2 F up 

swing 

2 

22
7/31/2011
 

TWH Set Temperature: 140 F / Shower @ 105 F / Mix @ 120 F 

Return 

Water 

Temp. 

Condensing

Technology 

Heating

System 

FACTORS INFLUENCING EFFECTIVENESS OF CONDENSING 

TECHNOLOGY 

SIMPLIFIED CONDENSING Chart 

80 

82 

84 

86 

88 

90 

92 

94 

96 

120 100 8060 140 160 180 200 

Dew Poin t o f N a t . Ga s 

Condensing 

N on-Conden sin g 

TW H ef f ic ienc y % 

TW H r et u r n w at er t emp o F 

98 

Qu est io n s? 

Qu est io n s? 

Qu est io n s? 

Qu est io n s? 

3 

23
 

 

Quietside 

QMV9 

Tempmizer 

Ai 

Handle 

Applying Water Heaters In Combination 

Space and Domestic Water Heating Systems 

July 31, 2011 

Balancing Performance with Customer 

Expectations 

July 31, 2011 

North American Climate Zones 

While the heating 

and cooling 

requirements vary 

across North 

America; everyone 

uses some type of hot 

water heater. 

Image from www.buildingscience.com 

July 31, 2011 

Multiple Sources of Hot Water 

History: Initial Market - Townhouse and condo 

Individual 

suite gas 

metering. 

July 31, 2011 

Integrated Field Installations 

Customer issue: reduced 

performance at draws of over 3 

gpm 

After correcting some 

installation faults (eg increase to 

3⁄4 piping, faster acting 

thermostat) 

Conducted multiple draw 

schedules. 

Use of small storage tank (20, 

30, 40 USG) to measure 

increased flow. 

Domestic 

Hot Water 

Pump 

Check 

Valve 

Domestic 

Cold Water 

Flue gas 

exhaust 

Air 

Intake 

r 

r 

24V to 

T-Stat 

120V/1ph/60Hz 

PRV to 

drain 

Gas 

T 

Hot 

Cold 

Mixed 

120V/1ph/60Hz 

120V/1ph/60Hz 

FR-5 

Controller 

T1 

T10 

T2 

T4 

T3 

T5 

T6 

T7 

T8 

T9 

Flow 2 

Flow 1 

T11 

Heat 

Engine 

Air 

Handler 

Capital cost reduction 

Squeeze into mechanical 

closets to gain more living 

space 

Created installation 

issues such as ventilation 

air, venting and piping 

Experience led to better 

designed mechanical 

closets 

July 31, 2011 

1 

24
 

. 

 

 

 

Addition of Small Storage Tank Innovation and Design Applications 

Industry has and will continue to 

provide the spark to develop 

products that will solve many of 

the issues. 

– New factory supplied systems that 

overcome mixed supplier conflict 

Affect overall efficiency, cost and 

maintenance 

– Cost of pump 

– Standby loss from piping 

– Unintended positive consequence: 

Freeze protection in harsh climate 

Storage tank design 

– Design modifications from standard 

storage tank to maximize performance. 

July 31, 2011 

– Design and controls methodology to 

maximize benefits (Consumer 

comfort, energy savings) 

Allow field design and creativity 

to overcome unique applications 

July 31, 2011 

Design Considerations 

Saving Money or Saving Energy 

Builder may side on lowest 

capital cost while the consumer 

(if educated) should prefer the 

lowest total life cycle costs 

Best way to save energy is to 

avoid the need in the first 

place. 

Furnace and Water Heater is 

the norm; need to educate on 

July 31, 2011 

other options 

Cycling Frequency and Short Cycling 

Regardless of product (heat 

engine or air handler); short 

cycling can lead to customer 

issues and premature failure of 

component parts. 

Pre-purge and post purge 

impact 

Condensing Considerations 

Balancing for Max Condensing requires 

controlling the air flow temperature 

– Cool air 

Control speed of air flow, use variable speed fans, 

ensure grill locations are appropriate 

Advanced duct design 

Air Handlers can run off geothermal systems at 

2 

July 31, 2011 

105F, so design is critical 

– Larger coils, however there is an economic tradeoff, 

– Pump flow controls to manage return water 

temperature control. 

July 31, 2011 

Run time to reach condensing 

mode 

Controls strategy is required 

to avoid cycling 

25
 

System Comparison 

Capital Cost Energy Use Total Life 

Cycle 

Costs 

Condensing Furnace and Water 

Heater 

$$$$ Energy 

usage could 

Need 

validated 

Air Handler + Condensing 

Storage Type Water Heater 

$$$ be 

equivalent 

based on 

total life 

cycle costs. 

Air Handler + Condensing 

Tankless 

$$$ design and 

application. Utility 

studies 

Condensing Boiler + Air Handler $$$$$ underway. 

Solar Pre Heat + Air Handler $$$$$ 

What work is needed to fill gaps and barriers 

Develop 3rd party programs to determine the 

benefits and application differences btwn various 

technologies 

– Impact on water usage 

– Electrical consumption 

– Consumer behaviour 

Training, then some more training at each level 

of the supply chain 

Provide industry guidance on best practices 

July 31, 2011 

Future 

From manufacturer’s view - volume is key 

Marketing ... entrenched furnace and water 

heater culture. 

– Need to define the benefits of the 

integrated system
 

Need to make the systems less complex at 

the field level. 

Control strategies to maximize comfort and 

energy savings.
 

July 31, 2011 

July 31, 2011 

Closing Thoughts 

Multiple condensing heat engine products will 

compete in the market. 

Each will need to find the right application for 

that technology 

Consideration for total life cycle costs 

Design and control strategy can overcome most 

performance issue 

Let innovation drive product development. 

July 31, 2011 

July 31, 2011 

Questions 

3 

26
 

 

 

 

 

 

 

 

 

 

 

 

 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 1reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Londonderry – January 6th, 2010 

Combination Space Heating - Addressing the Key 

Questions From a Manufacturers’ Perspective 

July 31st, 2011 

Tankless and Space Heating 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 2 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

 Current Experiences 

 Who? 

 What? 

 Tankless as a Heat Source 

 Cycle Frequency and Short Cycling 

 Hot Water Delivery Issues 

 Using Storage as a Manifold 

 Scale and System Debris 

 Combi-System or Traditional? 

 Future Knowledge 

2 

Agenda 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

Current Experiences 

 Who is installing open loop 

combination systems? 

 Smaller independent heating 

system companies 

 “Experts” from trial and 

error system design 

 Some larger plumbing 

companies 

 Experienced D-I-Y installers 

 Homeowners looking for a 

“cheaper” boiler 

Current Experiences 

 What types of systems are they 

installing? 

 Open Loop 

 Separated 

 Non-separated 

 Closed Loop 

 Water heaters used in boiler 

applications 

 Un-certified or questionable 

installations 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 3 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 4 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 5 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Open Loop 

Tankless 

Water 

Heater 

July 31st, 2011 

Tankless and Space Heating 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 6 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Open Loop - Separated 

Tankless 

Water 

Heater 

July 31st, 2011 

Tankless and Space Heating 

1 

27
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

Closed Loop – Boiler Application 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 7 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Tankless 

Water 

Heater 

Current Experiences – Issues and Concerns 

 Health 

 System stagnation 

 Use of non-potable system components 

 Safety 

 Failure to use scald prevention devices 

in high temperature application 

 Efficiency 

 Lack of condensing at high temperatures 

 No standards for efficient system design 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 8 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

Tankless as a Heat Source 

 Radiant Floor (98F – 120F) 

 Low temperature 

 Longer run times 

 Simple Controls 

 DHW priority is unnecessary 

 Air Handler 

 Mid to High temperature (140F+) 

 Shorter cyclical run times (< 10 minutes) 

 Complex Controls 

 Lack of DHW can cause “cold blow” 

Tankless as a Heat Source 

 Baseboard 

 Typically high temperatures (160+) 

 Lower temperature systems exist 

 Cast iron radiators corrode and can 

clog filters or components 

 Copper radiators common in newer 

systems 

 Longer run times 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 9 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 10 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

Tankless as a Heat Source – Short Cycling	 Tankless as a Heat Source - DHW Delivery Issues 

 Definition of short cycling 

 Run time less than 10 seconds 

 Potential effects on tankless 

 Wear and Tear 

 Is usable energy delivered? 

 Short Cycling is not usually found in space heating applications 

 Exceptions 

 Heat load << minimum firing rate of the appliance 

 Equipment malfunction 

 Improperly sized pumps 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 11 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

 Additional plumbing related to heating system 

 Benefit 

 Hot/Cold plug flow has more time to 

dissipate 

 Downside 

 DHW delivery time is increased in non 

heating times 

 Trickle flow 

 Trickle flow is possible during heating 

cycles 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 12 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

2 

28
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

Tankless as a Heat Source – Storage/Manifold 

 Un-powered tank 

 Could be designed similar to low loss header 

 Increases DHW delivery time (non heating cycles) 

 Decreases temperature fluctuations 

 Increases energy utilization slightly 

 During heating and DHW cycles 

 Powered tank 

 Decreases DHW delivery time 

 Decreases temperature fluctuations 

 Allows Trickle flow always 

 Increases energy utilization slightly 

 During off-cycles and trickle flow 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 13 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

July 31st, 2011 

Tankless and Space Heating 

Combi System or Traditional? 

 New Construction 

 Combi system can reduce overall cost of installation 

 Only one gas line to run 

 Smaller utility room 

 Opportunity for properly designed hydronic system 

 Retrofit 

 Must analyze ROI vs. installed costs 

 Existing system may not be suitable for tankless 

Tankless as a Heat Source – Scale and Debris 

 Scale 

 Combi systems pose very little additional concern regarding 

scale when compared to a DHW system 

 Debris (Sediment, thread tape, and sealant) 

 Small inlet filter can clog and decrease flow 

 Filter can be removed once thread tape and sealant leave the 

system 

 Y Strainer is another alternative to prevent clogging 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 14 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 16 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Radiant 

Floor 

Air 

Handler 

Base 

Board 

Condensing 

Tankless 

Condensing 

Combi-Boiler 

Rating Overall Rating Overall Overall 

Heating System

efficiency 

Heating System

Complexity 

System Efficiency

and Applicability 

Cond. Boiler + 

Indirect 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

July 31st, 2011 

Tankless and Space Heating 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 15 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 17 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Radiant 

Floor 

Air 

Handler 

Base 

Board 

Condensing 

Tankless 

Condensing 

Combi-Boiler 

Rating Overall Rating Overall Overall 

Heating System

efficiency 

Heating System

Complexity 

System Efficiency

and Applicability 

Cond. Boiler + 

Indirect 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

July 31st, 2011 

Tankless and Space Heating 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 18 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Radiant 

Floor 

Air 

Handler 

Base 

Board 

Condensing 

Tankless 

Condensing 

Combi-Boiler 

Rating Overall Rating Overall Overall 

Heating System

efficiency 

Heating System

Complexity 

System Efficiency

and Applicability 

Cond. Boiler + 

Indirect 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

July 31st, 2011 

Tankless and Space Heating 

3 

29
 

 

 

 

 

 

 

 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 19 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Radiant 

Floor 

Air 

Handler 

Base 

Board 

Condensing 

Tankless 

Condensing 

Combi-Boiler 

Rating Overall Rating Overall Overall 

Heating System

efficiency 

Heating System

Complexity 

System Efficiency

and Applicability 

Cond. Boiler + 

Indirect 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

July 31st, 2011 

Tankless and Space Heating 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 20 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Radiant 

Floor 

Air 

Handler 

Base 

Board 

Condensing 

Tankless 

Condensing 

Combi-Boiler 

Rating Overall Rating Overall Overall 

Heating System

efficiency 

Heating System

Complexity 

System Efficiency

and Applicability 

Cond. Boiler + 

Indirect 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

Heating System

efficiency 

Heating System

Complexity 

Domestic Water 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

July 31st, 2011 

Tankless and Space Heating 

Issues for the Future 

 Gaps 

 Actual system efficiencies when using alternative heat sources 

 Hybrid Water Heaters 

 Questions? True effect of small volumes of stored water 

 Effect of water pre-heat systems on total system efficiency 

 Solar, Heat Pump, etc. 

 Control Systems for non-boiler heat sources 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 21 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

Thermotechnology 

07.31.2011 | © Bosch Thermotechnology 2010. All rights reserved, also regarding any disposal, exploitation, 22 reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 

4 

30
  

       

       

     

   

   

     

     

   

       

                   

                   

     

         

   

                      

                 

   

         

       

   

       

         

           

             

       

         

       

           

             

           

           

         

   

7/31/2011

Installing Combination Systems:

Optimized Designs and Potential

Project Funding: Performance Problems – Sustainable Resource Center, Minneapolis, MN

Ben Schoenbauer • DOE SERC Grant

Center for Energy and Environment – Building America – NorthernSTAR Team

Minneapolis, MN

How We Got Here Federal Innovation Grant •	 Sustainable Resource Center

– Federally funded weatherization	 • Sustainable Energy Resources for Consumers Grant.

• Low‐income housing, single & multi‐family •	 Innovation grant from stimulus funding •	 Energy retrofits must pay for themselves in energy savings over

their lifetime. • No SIR requirements

• $6500/home average •	 Evaluation of actual energy savings •	 2‐3 hour Audit & diagnosis, mechanical retrofit, air sealing &

insulation inc. H&S, inspection • Recognizes higher cost of new technologies

• ASHRAE 62.2, tightness limits, pressure diag. •	 Already awarded to 5 agencies in MN – Combustion Safety PROBLEM •	 Pays for installation in over 400 homes state‐wide • Many retrofits with 95% 2 stage ECM furnace ~$3500 + 65% •	 13 month duration, starting now power vented DWH ~$1500 – for H&S, less than 10% better

Project Overview

•	 400+ residential installations by March 2012

– Needed to scale up fast

•	 Many contractors had very little experience

and were installing appliance out of the box

•	 Added an initial phase of “Lab” installations

– To determine best practices for existing

equipment installations

– To demonstrate systems to contractors, codes

people, utilities, etc

1

Lab Testing

http://srcefficiencylab.tumblr.com/

31
     

               

       

         

   

                 

     

   

         

   

       

   

                 

     

   

7/31/2011
 

Equipment • 4 Boilers

– Two low mass boilers

– Two boilers with integral DHW tanks (6, 12 gallons)

• 2 condensing tankless water heaters

– One with 2 gallons of storage

• 3 condensing tanks

– 100 btu/hr input with 34, 50, and 50 gallon storage

– One with modulating burner

• 6 hydronic air handlers

– Two with built in ventilation

Lab Testing ‐ Protocol

• Heating Plant Testing

– Idle tests

– Simulated air handler return

• Air Handler Testing

– Output capacity over a range of flow rates and

temps

• Full System Tests – Performance Tests

– Max capacity testing

– Cyclical testing

Idle Testing

2

32
   

   

             

     

   

7/31/2011
 

Boiler 4

TWH 2 ‐ hybrid

TWH 1

Work Horse

Heating Plant

TWH

Sim AH Test

Heating Tested

Heating Plant

TWH

TANK

BOILER

DHW

Supply Supply

Return Return

Electric Gas

Air Handler Capacity Tests

Work Horse

Heating Plant

TWH

Heating

Tested

Air Handler

Air

Return Return

Supply Supply

Electric

3

33
   

               

           

   

                 

           

  

           

   

     

     

     

   

   

Parasitic power consumption

   

7/31/2011
 

Air Handler Tests

•	 Check the performance of the air handlers in

the lab versus the specification sheets

provided by manufacturers

•	 Determine for each AH the heating load it can

meet at desired air and water temperatures

AH 3 Results

AH is rated for 60,000 Btu/hr heating

AH 3 Results

• Allowing Settings so that

• Return Water T <107

• Supply Air T >105

– Outputs around

40,000Btu/hr

• Options are limited

Full System Demo

4

34
   

   

       

       

       

       

       

       

       

     

7/31/2011
 

Failure Mode Tests

~4 °F dip

• 2.0 gpm on for 40 seconds

– No draw for 6 minutes

• 1.1 gpm on for 20 seconds

– No draw for 1 minute

• 1.1 gpm on for 12 seconds

– No draw for 7.5 minutes

• 1.2 gpm on for 55 seconds

BOIL4 was always hot

Tankless Combi Efficiecny

5

35
   

           

         

           

     

   

             

                 

             

          

               

   

       

         

   

               

           

7/31/2011
 

Upcoming: Field Installations

• 400 installs in Minnesota before March 2012

– Detailed Pre/Post monitoring on 20 sites

– Utility Bill analysis on all 400 sites

• System selection based on:

– Space Heating Load

– Perceived DHW load (both daily usage and

simultaneity)

– Water hardness

– Cost

Field Installations: Systems/Cost

• Data from 8 sites with completed installs and bills submitted

Mostly sites with high water hardness which

effected product selection. High water

hardness will not be a concern for all homes.

Installation Costs

• Multiple speed ECM fluid pumps

boiler based systems

prioritization

controls

Issues to Consider

• Primary secondary loop configuration for

• Air handlers with fan cut out for DHW

• Integrated system packages with built in

6

36
 

 

 

 

 

 

 

 

 

7/31/2011
 

Progress On Improved Testing and Rating Standards 

for 

Combination Space and Domestic Water Heating 

Prepared By: Martin Thomas & Rosalyn Cochrane, 

Natural Resources Canada 

For: Building America Expert Meeting, July 31, 2011 

Definition: 

 Combined space and water 

heating system (“combo”) 

— a product or a group of 

individual components that form 

an integrated system that is 

designed to provide space 

heating and water heating. 

 Note: We discourage the use of 

“Combos” based on noncondensing tank water heaters + 

fan coils. 

Combination System Layout 

- Segregated Space & DHW Heating Why Build a Combination System? 

 Integrating the space & water heating functions can 

lead to synergistic efficiency benefits. 

 As space heating loads drop, the water heating load 

becomes more significant; with EE housing, overall

the two loads become comparable 

 The combination and flexibility offered with the two

loads can allow for the technology to be suitable for

low energy or near net-zero housing. 

 Venting & gas/fuel connections are simplified 

resulting in a compact, potentially lower cost, 

installation. 

Test Methods Available 

In North America there are two* test 

Methods Available: 

 ASHRAE 124 – 2007 

 Covers Gas, Oil & Electric, Forced Air & 

Hydronic. 

 Yields a Combined Annual Efficiency (CAE) 

 CSA P.9 – 2011 

 Covers Gas & Oil, Forced Air only. 

 Yields a Thermal Performance Factor (TPF) 

Differences Between the Two Test 

Methods 

With ASHRAE 124 : 

 there is no way to assess the combined 

performance, i.e. Testing a combo as an operating 

system, not individual components. 

 Combo may be rated under unrealistic conditions. 

 Test does not evaluate the complete system and 

recognize performance interactions and synergies 

 Smart integration 

* There is also ASHRAE 206. 

 Advanced controls 

1 

37
7/31/2011
 

Differences Between the Two Test 

Methods 

With CSA P.9 : 

 Doesn’t force set points, which allow 

manufacturers to be creative with controls. 

 Tests and rates at the conditions in which the 

system operates, as opposed to being tested to 

current test methods that are strictly applicable to 

that component. 

 Two Part load efficiencies in space heating mode 

(plus maximum input rate). 

The CSA P.9 in More Detail 

System Categories: 

 Type A System: a combo with a fixed capacity for 

space heating;
 

 Type B System: a combo equipped with controls that 

automatically adjust the space heating capacity 

based on the space heating load; and 

 Type C System: a combo with a thermal storage 

tank or equivalent that decouples the space heating 

load from the burner control. 

 Separate combined duty test. 

The CSA P.9 in More Detail 

Currently does not apply to: 

 Hydronic distribution (Future work for P.9) 

 Electric and solar-based combo systems; 

 Not test-verified for oil yet. 

 solid-fuel-based combo systems; and 

 multi-family dwellings with a central 

heating plant
 

The CSA P.9 in More Detail 

 Overall performance factor needs to aggregate 

performance in each operating condition 

 Consistent set-ups required and equipment 

functions need to be fully operational during all 

tests 

 Controls need to be operational during 

performance testing 

 Space heating needs to include (weighted) 

part-load fractions 

P.9 Performance Descriptors 

 Thermal Performance Factor (TPF) 

 Composite Space Heating Efficiency 

(CSHE) 

 Water Heating Performance Factor 

(WHPF) 

 1 hr Water Delivery Rating (OHR) 

Space Heating Performance 

 Input-Output air enthalpy approach 

 Part load testing and rating based on loadweighted performance measurements 

 Part load space heating cyclic tests 

15%, 40% and Full load output, 

 CSHE =0.1xEff(100%)+0.6xEff(40%)+0.3xEff(15%) 

 Takes into account the energy input delivered 

to the airstream (excludes casing/pipe losses) 

2 

38
 

 

 

 

 

7/31/2011
 

Water Heating Performance 

 Water enthalpy method (energy out / energy In) 

 24 hr simulated use test and recovery efficiency 

 Combo capacity as a water heater determined 

and reported as a one (first) hour rating 

 Additional capacity testing done with and without 

concurrent calls for space heating (Combined 

operation) 

 Same as CSA P.3, ASHRAE 118.2, or US DOE 

Overall Performance Rating 

Thermal Performance Factor (TPF) 

TPF = 2000HCAP + 4400 

[2000HCAP/CSHE] + [4400/WHPF] 

2000 = an annualized aggregate rating of the number of full-load

operating hours of the combo in space heating mode, h 

HCAP = full-load space heating system output, kW (Btu/h) 

4400 = annual domestic hot water draw load based on the standardized water heating simulated use test (SUT), kWh 

(Btu) 

CSHE = composite space heating efficiency 

EF test. WHPF = water heating performance factor 

The ASHRAE 124 in a Nutshell 

 Uses ASHRAE 103 to test Hot Water Generator as a 

boiler to get Effyhs = space-heating seasonal efficiency

(%) under fixed test conditions. 

 Tests at minimum and maximum heat input. 

 Uses ASHRAE 118.2 (or 118.1) to establish water 

heating efficiency (EF). 

 Uses weighting factors based on: the temp. base for 

HDD = 65°F, US ave. outdoor temp. over heating 

season = 42°F, US ave. outdoor heating design 

temp. = 5°F, oversize fraction = 0.7 and the ratio of 

energy delivered in hot water to the maximum possible 

energy use per day. 

The ASHRAE 124 in a Nutshell 

Combined Annual Efficiency, CAE
 

CAE = [(SHF × Effyhs/100) + (WHF × Effyss/100) + (R × NHF × EF)]
 

[(SHF) + (WHF) + (R × NHF)] 

Where: 

SHF = Space Heating Factor 

WHF = Heating Season Water Heating Factor 

NHF = Non-Heating Season Water Heating Factor 

EF = Water Heater Energy Factor 

Effyhs = Space-Heating Seasonal Efficiency 

Effyss = Steady State Space-Heating Efficiency 

R = ratio of non-heating-season days to heating-season days 

Technologies tested? 

 Combo 1: Power vented non-condensing storage 

WH coupled with (48,000 Btu/h) air handler with 

ECM motor. (40 MBtu/h input / 50 US Gal.) 

 Combo 2: Power vented condensing commercial 

storage WH coupled with same air handler as 

Combo 1. (76 MBtu/h input / 50 US Gal.) 

 Combo 4: Manufactured unit, Condensing low 

mass boiler / 25 to150 MBtu/h input plus fan coil 

with ECM motor, Modulating, and DHW Priority. 

1. 

3 

39
7/31/2011
 

2. 4. 

Lab. Test Results 

Results Comparison 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0.8 

0.9 

TPF CSHE WHPF 

Combo 1 

Combo 2 

Combo 4 

Combination System Performance 

Lets Look at Some Field Test Results 

The Canadian Centre For Housing Technology (CCHT) 

Combination System Performance 

Testing at the CCHT 

Combo 4 ēKOCOMFORT 

Combination System Performance 

Rating Performance 

ASHRAE 124 CAE Values 

Reference System (Estimated) = 85 % 

Combo 1 = 74% 

Combo 2 = 85% 

Combo 3 = 76% 

Note that the CAE is weighted heavily towards the space 

heating efficiency and in this case it does not accurately 

reflect the superior performance of the Condensing 

Furnace for space heating. 

The ASHRAE 124 is 

currently being revised 

4 

40
 

7/31/2011
 

Combination System Performance 

Testing at the CCHT 

Combo 4 ēKOCOMFORT 

CAE = 74 % 

CAE = 85 % 

CAE = 76 % 

CAE = 85 % 

Combination System Performance 

P.9 Results 

Testing on 3 combination systems has been conducted: 

(1) A combination system based on a water Heater having 

a recovery efficiency of 71 % - Similar to Combo 1; 

TPF = 0.57 

(2) A combination system based on a water Heater having 

a recovery efficiency of 90 % - Similar to Combo 2; and 

TPF = 0.68 

(4) A packaged eKocomfort combination system with a 

steady state efficiency of 95%. 

TPF = 0.83 

Combination System Performance 

Testing at the CCHT 

ēKOCOMFORT 

TPF= 0.57 

TPF= 0.83 

TPF= 0.68 

The TPF provides a 

better rating than 

the CAE. 

Combination System Performance 

Next Steps 

The water heating portion of the 

test needs to be revised to reflect 

current “Real Use”. 

Simplified Draw Patterns 

0 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 

Time of Day (hour) 

Volume of Hot water Drawn (Litres) 

Low 

Medium 

High 

Time Between Draws - A - 8h 

0 

50 

100 

150 

200 

250 

300 

5

20

35

50

65

80

95 110 125 140 155 170 185 200 215 230 245 260 275 290 305 320 335 350 365 380 395 410 425 440 455 470 485 500 515 530 545 560 575 590 605 620 635 650 665 680 695 710 725 740 755 770 785 800 815 830 845 860 875 890 905 920 935 950 965 980 995 1010 1025 1040 1055 1070 1085 1100 1115 1130 1145 1160 1175 1190 more 

Time Between Draws(s) 

Frequency of Occurance 

0.00% 

2.00% 

4.00% 

6.00% 

8.00% 

10.00% 

12.00% 

14.00% 

16.00% 

Percentage 

Frequency 

Percentage 

Draw Volumes - A - 8h 

0 

20 

40 

60 

80 

100 

120 

140 

5 10 15 20 25 30 35 40 45 50 more 

Draw Volumes (L) 

Frequency of Draws 

0.00% 

5.00% 

10.00% 

15.00% 

20.00% 

25.00% 

30.00% 

35.00% 

40.00% 

45.00% 

50.00% 

Percentage

Frequency 

Percentage 

Combination System Performance 

Next Steps 

(1) The ASHRAE 124 is currently being reviewed with a 

view to making some improvements 

(2) It is possible that we could take elements from the CSA 

P.9 and incorporate them into the ASHRAE 124 and 

also develop a suitable test for under-floor or radiator 

based hydronic heating systems, that could be added to 

the CSA P.9 

(3) We are also considering modifying the draw schedule 

for water heating to more properly reflect today’s reality 

of hot water use (in CSA P.3 & ASHRAE 118.2). 

Next Steps 

 Further testing of different heat 

generators: 

 Tankless water heater 

 Condensing tankless water heater 

 Boilers, including Oil 

 Oil storage water heaters 

 Inclusion of test for hydronic distribution 

systems 

5 

41
7/31/2011
 

QUESTIONS Contacts: 

 Martin Thomas, 

(613) 947 0067 or martinth@nrcan.gc.ca 

 Rosalyn Cochrane, 

(613) 995 5433 or rocochra@nrcan.gc.ca 

6 

42
7/31/2011

1

The Science of Water Heating from a 

Plumber's Perspective 

The Museum 

The Collection Sediment 

The 

Galvanic 

Series 

Erosion 

43
7/31/2011

2

Dezincification Dielectric - side 

Dielectric - end Steel vs Brass 

Brass & Steel 1 Brass & Steel 2 

44
7/31/2011

3

Glass at Drain Plugged Relief 

Recirc w/ Copper Slow Leak 

Lawnmower Backdrafting 

45
7/31/2011

4

Fix for Odor Nice Drain 

Old Lined Nipple 

46
8/22/2011
 

Field Experience with Tankless Hot Water Heaters 

Used in Combination Space and 

Domestic Hot Water Heating Systems 

By: 

Armin Rudd 

Building Science Corp 

717.867.0123 

arudd@buildingscience.com 

www.buildingscience.com 

For: 

Combi system expert meeting 

Westford, MA 

July 31, 2011 

Building Science Consortium Building Science Consortium 

Building Science Consortium Building Science Consortium 

Building Science Consortium Building Science Consortium 

47

1 
 

 

 

8/22/2011
 

Dried mineral precipitate from inlet strainer 

Building Science Consortium 

Combi system with non-condensing gas-fired tankless heater 

(PA installation with tankless heater pre-strainer added) 

Building Science Consortium 

Building Science Consortium 

Wire Screen Mesh versus Micron Comparision Chart 

Mesh Micron 

5 3000 

7.5 1980 

10 1480 

16 975 

20 750 

30 500 

40 375 

50 300 

60 238 Rinnai inlet strainer 60 mesh, Shelco strainer 230 micron 

80 175 CAT Pumps strainer 80 mesh 

100 149 

140 100 

200 74 

250 60 

270 50 

325 40 

400 35 

Building Science Consortium 

Building Science Consortium Building Science Consortium 

48

2 
 

8/22/2011
 

Mineral precipitate and crystals collected on Shelco 230 micron strainer, after 

about one year. Would have clogged the Rinnai strainer many, many times. 

Building Science Consortium Building Science Consortium 

Building Science Consortium Building Science Consortium 

Building Science Consortium 

Combi system with non-condensing gas-fired tankless heater 

(PA installation with water conditioner added) 

Building Science Consortium 

49

3 
 

 

 

 

 

 

 

 

 

8/22/2011
 

Building Science Consortium 

Scale removed from galvanized dielectric union fittings weeks after 

installation of electronic water conditioner 

Building Science Consortium 

Combi system with condensing gas-fired tankless heater 

(Installed in NYSERDA Utica, NY project in Fall 2010) 

Building Science Consortium 

Combination space and domestic hot water heating system with tankless gas 

water heater and small storage/manifold tank. Installed at NYSERDA deep 

energy retrofit project in a 2-family building in Utica, NY. 

Building Science Consortium 

Rinnai RC 80 H.P.I O.D.H. 

Rinnai 045 AHB Hydronic Air Handler (ECM fan) 

Building Science Consortium 

Cost (sealed bid) 

Group [A] Heating system 

Labor: $1,728 plus Materials: $5,000 

Group [A] 

2 Rinnai RC 80 H.P.I O.D.H. 

2 plumbing kits 

2 termination kits for Rinnai 

2 10” vent extensions (polypropylene) 

2 whirlpool 12 gallon hot water tanks 

2 Therm-x-trol St-5 expansion tanks 

2 i m xing valves 

2 clearwave H.D. electronic water conditioners 

2 Y strainers- Watts 351 M (stainless steel) 

2 taco Brass 007 Pumps 

2 Taco S.S. 013 Pumps 

2 Rinnai 045 AHB Hydronic Air Handler 

4 Flow check Valves 

2 1⁄2” Drain valves 

14 3⁄4 “ ball valves 

2 Lex Pro 511 C T-Stat 

All copper tubing and fittings to complete install 

All electrical wire and boxes, switches, breakers 

Building Science Consortium 

50

4 
(gal/day) (cycles/day)

04/02/1104/07/1104/12/1104/17/1104/22/1104/27/1105/02/1105/07/1105/12/11

Temperature (F)

100102104106108110112114116118120

40 60

80

60 100

120

Runtime (s/min)

Sys 1 Sys 2

Building Science Consortium Building Science Consortium 

System without tank has wide range of supply air temperature 

Water heater cycles per day was much higher without the tank 

System 1 (no tank)

Tankless heater daily cycles 120 200

180

180 100 160 160

140 140 80

5 100

0 50

0

150

200

04/02/1104/07/1104/12/1104/17/1104/22/1104/27/1105/02/1105/07/1105/12/11

(h/day)

10

15

04/02/1104/07/1104/12/1104/17/11 Sys 1 Sys 2 04/22/11 04/27/1105/02/1105/07/1105/12/11

Building Science Consortium Building Science Consortium 

Sys 1 Sys 2

Julian Day of 2011

Tsupply air Treturn air Water heater runtime Heating runtime

Combi system with condensing gas-fired tankless heater, Same operational problems with inlet strainer clogging, Small storage tank removed plus more! (modified in NYSERDA Utica, NY project in Winter 2011) 

Building Science Consortium Building Science Consortium 

Hot water consumption was higher for System 1 (no tank) Water heater daily runtime was similar for both systems 

Tankless heater daily runtime Daily domestic hot water consumption 25 300

20 250

40 40 20 20 20

0 0 0

8/22/2011
 

5 

80

100

120

60

51
80

100

120

20

40

60

60

80

8/22/2011
 

Hot water draw rate (F)

Building Science Consortium 

Data Collection 

Output 

channel 

# Name Description Units Sensor 

1 Array ID (indicates type of data output as: 1 s, 1 min, 1 h, 1 day, or equipment on/off status) 

2 Year 

3 Jul day 

4 h/min 

5 sec 

6 Tret heating return air temperature (F) Type T thermocouple 

7 Tsup heating supply air temperature (F) Type T thermocouple 

8 Tmains mains water temperature (F) Type T thermocouple 

9 Tmixout mixing valve water temperature (F) Type T thermocouple 

10 Thtsup heating coil inlet water temperature (F) Type T thermocouple 

11 Thtret heating coil outlet water temperature (F) Type T thermocouple 

12 Tdhwhtrin water heater inlet temperature (F) Type T thermocouple 

13 Tdhwhtrout water heater outlet temperature (F) Type T thermocouple 

14 ahuNow air handler unit on/off status Veris current sensor 

15 whtrNow water heater on/off status Veris current sensor 

16 ahuRT air handler unit runtime (s) Veris current sensor 

17 whtrRT water heater runtime (s) Veris current sensor 

18 ahuCycles air handler unit on/off cycles Veris current sensor 

19 whtrCycles water heater on/off cycles Veris current sensor 

20 ahuWh air handler unit electrical energy (W-h) IMS true RMS watt-hour meter 

21 whtrWh water heater electrical energy (W-h) IMS true RMS watt-hour meter 

Omega water flow meter 

22 dhwFlow water heater water flow (gal) 75 pulse/gal 

AC-250 temperaturecompensated gas meter 

with IMAC pulser .125 ft3 23 natgas water heater gas flow (cf) /pulse 

Building Science Consortium 

T mains T htr,out T mix,out

Building Science Consortium 

Hot water draw (gpm)

Thank you! 

Questions? 

Temperature leaving mixing valve (F)

0

0.5

1

1.5

2

2.5

3

3.5

40

20

0

4/24/11 00:27:224/24/11 00:28:484/24/11 00:30:144/24/11 00:31:414/24/11 00:33:074/24/11 00:34:344/24/11 00:36:004/24/11 00:37:26

0 0

10

100

120

140

Temperature (F)

100102104106108110112114116118120 40

80

60

100

120

180

160

140

Runtime (s/min)

Temperature leaving mixing valve (F)

Temperature (F)

1 20

0.5

1.5 30

50 2 40

60 2.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

20

40

60

80

100

120

Hot water draw (gpm)

System with tank has narrow range of supply air temperature 

System 2 (with tank)

System1 (no tank)

Temperature leaving mixing valve vs.Drawrate

200

140

20

0 0 0

Julian Day of 2011 Hot water draw rate (F) Tsupply air Treturn air

Water heater runtime (s/min) Heating runtime (s/min)

Building Science Consortium Building Science Consortium 

System without tank provides room temperature water at low draw rates 

System1 (no tank)

System2 (tank) 10 minutes of on/off draw w/o heaterturning on Temperature leaving mixing valve vs. Drawrate 80 3.5

160 70 3

Building Science Consortium 

52

6 
DOE/GO-102012-3483 ▪ July 2012

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