Homeowners with natural gas water heaters have difficulty justifying the expense of a more efficient condensing heater. Combination space and domestic hot water systems bundle together the two loads, which saves energy and makes them more cost-effective. These systems also help eliminate combustion safety concerns.
Historically, mechanical contractors have custom engineered and pieced together combi systems in the field, paying little attention to efficiency and optimization. But condensing heating plants will only reach their energy saving potential when all components are designed and installed correctly.
Performance and Optimization of Residential Condensing Combi Systems
1. Performance and Optimization of
Residential Condensing Combination
Space and Water Heating Systems
Ben Schoenbauer, Center for Energy and Environment
April 23, 2013
2. Sponsors and Partners
NorthernSTAR - A DOE Building America Research Team
Sustainable Energy Resources for Consumers Grants
Center for Energy and Environment
Sustainable Resources Center
University of Minnesota
The Energy Conservatory
3. Overview
Background: Project and Equipment
System Design
Field Results: Efficiency, Savings, Comfort
Cost
What’s next
4. How this project came about
− Weatherization is able to seal homes tighter and tighter
− Leads to combustion safety issues
− Requires sealed combustion
− Requirements on Savings vs installed cost rule out high
efficiency water heaters
− Forced to use safety budget to install 60% direct vent tanks with
very little energy savings
− SRC got a SERC grant to look at using a DIA
5. What is a Dual Integrated Appliance?
A. A mechanical system that uses one heating plant (natural gas
burner) to provide both space heating and hot water
B. Space heating side can be either hydronic or forced air
C. Systems can use a closed or open heating loop
This project will look at natural gas forced air DIA systems. Boiler
based systems will be closed loop and water heater systems
have an open loop.
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10. Page 10
PROBLEM
+ Some contractor’s had little experience
+ System schematics often developed on site
+ Little or no sizing information provided
+ System components came from several
manufacturers
+ Manufacturer’s settings typically do not lead to best
performance
+ Decided to design and optimize systems in a
laboratory
+ Could then provide contractors with more detail
installation guidelines
Installation and Sizing
11. Page 11 Full report at:
http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/labtests_combi_spacewh.pdf
13. Page 13
Air handler performance
+ Hydronic coil transfers heat
from water to air
+ Goals:
+ Return water <105 °F
+ Delivered air >110 °F
+ Goals must be balanced with
capacity needs
+ Installation parameter charts
were developed for each air
handler
23. Page 23
+ Locations and equipment size may change
+ Tankless water heaters and combi boilers are
often wall mounted
+ Location of the large gas line may change
+ Additional power lines
Installation:
25. Page 25
Adjusting the water flow rate through the air handler
Installation: Equipment Set Up
26. Page 26
Adjusting the air flow rate through the air handler
Installation: Equipment Set Up
Most Common Methods:
• Dip switches
• Switching wires for various
speeds
28. Page 28
Existing Equipment
DHW Loads
Cold In from Mains
Hot Space
Heating Air
Runtime
Air Temp
Ambient T
Gas
ND Tank
Water
Heater
Electric Gas
Single
Stage
Furnace
Conditioned
Space
29. Page 29
DIA Installation
DHW Loads
Cold In from Mains
Supply to AH
Return from AH
Hydronic
Air
Handler
Hot Space
Heating Air
Water Temp
Water Flow
Consumption
Air Temp
Air Flow
Electric
Ambient T
Electric Gas
Water
Heater
Conditioned
Space
42. Page 42
Power Consumption
+ During Space Heating
+ Existing Systems: 550 W
+ Combi System: 475 W
+ During Continuous Fan Operation:
+ Existing Systems: 425 W
+ Combi Systems: 50 W
50. Page 50
Note:
• Typical loads were 25,000 Btu/hr design day space heating loads and 40 GPD hot water.
• Base Case: $725 per year gas bill (915 therms)
Savings and paybacks
51. Page 51
Savings and Paybacks
Note: Combi systems were cheaper to install that
a condensing water heater and condensing
furnace
52. Page 52
+ System Controls: Work to be completed in 2013
+ What cycle lengths are necessary to prevent short cycling for
efficiency? Room temperature?
+ How will fan and pump modulation improve efficiency and
comfort?
+ How much can temperature set backs (outdoor resets) improve
performance?
+ How will system performance change if we remove the air
temperature restrictions?
+ Other Equipment Needs
+ Improvements to air and water temperature delays
+ DHW priorities impact on comfort
+ Other Program Needs
+ Method for verifying savings for rebate programs
+ Consistent rating system for combi systems
+ Impacts on cost
What else do we need to know?