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HUMIDIFICATION RETROFITS DELIVER
RESIDENTIAL FURNACE EFFICIENCY
Retrofitting 80% Residential Furnaces for High Efficiency
Josh Quinnell, Ph.D.
Thursday, December 14, 2017
Conservation Applied Research and Development (CARD) Grant # 85907
Pg. 2
Outline
• Introduction• Background
• Research Objectives
• Methodology• Characterization & site selection
• Measurements & data acquisition
• Analysis
• Results• Performance
• Humidity
• IAQ
• Cost Effectiveness
• Conclusions & Recommendations
Pg. 4Pg. 4
Forced Air Heating: 80% or 90%+
High efficiency condensing furnace (90%+)Standard efficiency furnace (80%)
Pg. 5
Energy Savings in Residential Heating
• The single biggest energy savings opportunity in MN
• 1/3 natural gas used in the residential sector
• 2/3 of that natural gas is used for space heating
• ~20% of MN natural gas used by forced-air furnaces
• Energy savings require an upgrade from standard
efficiency (80%) to condensing furnace (90+%)
• A few problems with furnace upgrades:
• Standard efficiency still commands 30%+ of the market
• Long-lived (20 – 30 years) appliances that achieve nameplate
performance until failure
• Either wait for failure or replace a working appliance
Pg. 7
Transport Membrane Humidifier (TMH)
• Gas Technology Institute (GTI) developed whole-house humidifier
• A second heat exchanger retrofitted to a standard efficiency furnace
• Ceramic tubes transport liquid water and heat from the flue gas to the
return air
• The nano-engineered ceramic membrane tubes transfer water and
block transport of other combustion products
• Devices promises to humidify and increase furnace efficiency
Pg. 10
Humidification
• Extreme dryness has negative consequences
• General discomfort (lower apparent temperature)
• Respiratory and skin irritation
• Static discharge
• Cracking & creaking of contracted wood
• Humidification has its own challenges
• Humidification requires a significant amount of energy for
evaporation (e.g. up to 20% of the heating load)
• Humidifiers (and excess humidity) are associated with many
problems including mineral deposition, microbial growth, and
health issues
Pg. 11
Objectives
• Validate the performance of TMH units and assess its
potential as an alternative path to high efficiency space
heating
• Measure the humidification benefits of TMH
technology and its performance as a whole-house
humidifier
• Monitor indoor environments to understand the
humidification benefit and adverse consequences of
excessive humidification
Pg. 13
Methodology
• Identify site selection variables influencing TMH
outcomes
• Design & install prototype TMH units in research sites
• Measure TMH field performance and perform long-
term monitoring of units and indoor air conditions
• Analyze performance, humidification benefits, and
energy savings
Pg. 14
Site Selection
• Furnace type/make/model/age
SiteFurnace
MakeModel
Age(yr)
Size(BTU/hr)
AFUE(%)
Airflow(cfm)
h2 Bryant 383KAV 16 88,000 80.6 915
h3 Rudd UGPH07EAVER 19 75,000 80.6 960
h4 ArcoAire GUA080A012AIN 27 80,000 80 870
h5 Goodman GMPV075-1.5/3 21 75,000 80 821
• Emphasis on indoor humidity conditions
• Occupant Density: humidity generation
• Envelope Leakage: rate of humidity removal
Pg. 16
Instrumentation
1
2
3
4
5
6
7
8
9
#
#
#
Furnace Runtime
Attic Space Temperature, Humidity, and Wood Moisture
Basement Space Temperature, Humidity, and Wood
Moisture
Common Space Temperature, Humidity, and Wood
Moisture
Ongoing Household Measurements
Characterization Measurements
Ongoing Furnace Measurements
Supply and Return Duct Pressures
House Envelope Tightness
Furnace Airflow
Supply Air Temperature
TMH Flue Gas Temperature (Out)
TMH Flue Gas Temperature (In)
TMH Temperature and Humidity
Return Air Temperature and Humidity
• Instrument furnace, TMH, and
dwelling
• Measure sensible energy added
by furnace & TMH
• Measure latent energy added by
TMH
• Measure temperature, humidity,
and moisture storage in home
• Analyze:
• Output rates (Btu/hr)
• Steady-state efficiency (%)
• Changes in indoor environment
Pg. 17
Code Compliance & Permitting
• Discomfort by building official over unlisted devices
• Permitting negotiations resulted in one year delay for
three installations
• Ultimately issued temporary installation permits in two
municipalities
• Documented performance & safety lab testing for each unit
• Installation instructions and operating manual for each site
• A P.E. report certifying the design & safety of the TMH
• Underwriters Laboratories field certification for one unit
Pg. 18
Installation
• Emphasis on documenting installation
• Retrofits will require fast and cheap installs
• Develop installation documentation
• Observe & document all installs
• Recruited a contractor and used a single crew
• Understand labor costs of installation
• Determine any barriers to installation
• Describe learning curve associated with installation
Pg. 25
Field Data
TMH BypassSite
DaysFurnace Cycles
DaysFurnace Cycles
h2 7 40 126 1594
h3 139 1550 68 604
h4 194 2474 173 1248
h5 118 1174 65 856
• Monitored for 1 – 2 heating seasons per site
• Alternate mode testing (TMH and bypass modes) in all seasons
• Reached design conditions
• Collected data during thousands of furnace cycles during both TMH
and bypass mode
• Net Result:
• Large quantity of data over
a large range in operating
conditions for four different
furnaces
Pg. 28
Performance Summary
• Space Heating
• 9% natural gas savings for space heating (5,300 Btu/hr)
• 5 – 7°F temperature increase across the TMH
• Humidification
• 9% natural gas savings if displacing other humidification
systems (5,200 Btu/hr)
• May not displace all energy for humidification if other
humidification systems remain operational
• If TMH does not displace previous humidification there are no
savings, but it remains a significant non-energy benefit.
Pg. 29
Humidifier Performance
• Median humidity
outputs of 10 – 21
pints/day
• Maximum humidity
outputs of 23 – 55
pints/day
• Typical outputs range
between 8 – 28
pints/day
Hu
mid
ifie
r O
utp
ut
(pin
ts/d
ay)
Pg. 30
Dynamic Humidifier Output
• More humidity in
cold weather
• No humidistat
control
• Humidity output
proportional to
runtime and
humidity difference
• Self-limiting nature
decreases over
humidification
concern
Pg. 33
Effect on Indoor Conditions
• TMH improves indoor humidity by 10% during cold weather (<32 ᵒF) and dry conditions (<30% RH)
• Over humidification avoided in mild to warm weather (>32 ᵒF)
• Outdoor humidity is a more important factor for determining
indoor humidity than humidifier output
• Overall output is reduced in home with baseline
relative humidity (40 – 50% RH)
Pg. 34
Energy & Cost Savings
Heating Only Heating and Humidification
Site therms Low Medium High therms Low Medium High
h2 158 $79 $126 $189 207 $103 $166 $248
h3 121 $61 $97 $145 285 $142 $228 $342
h4 71 $36 $57 $86 207 $104 $166 $249
h5 94 $47 $75 $113 167 $83 $134 $200
• Furnace performance increase readily applied to
weather-normalized loads
• Savings sensitive to heating load and gas prices
• Savings double with humidification
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Total Installed Costs $1,400 - $1,900
Low High
Production Cost $402 $625
Retail Price $603 $938
Misc. Materials $306 $306
Install Labor $459 $660
Total Installed
Cost$1,368 $1,904
Pg. 36
Payback Scenarios at $1,400
Heating onlyHeating and
Humidification
Potential rebates:
Space heating conservation
Humidification conservation
Humidifier displacement
$200 $400
Site Low High Low High Low High Low High
Scenario 1 17.3 7.2 13.2 5.5 11.3 4.7 9.4 3.9
Scenario 2 22.6 9.4 9.6 4.0 8.2 3.4 6.8 2.8
Scenario 3 38.3 16.0 13.2 5.5 11.3 4.7 9.3 3.9
Scenario 4 29.1 12.1 16.4 6.8 14.0 5.8 11.6 4.8
• Nominal lifetime: 12 – 15 years (underlying furnace)
Pg. 38
Conclusions
• TMH adds 10,500 Btu/hr to standard efficiency furnaces
• Offers direct natural gas savings of 9% for space heating and 9%
for humidification
• Performs similarly to a whole house humidifier without the
headaches of those systems
• It operates passively; output is proportional to need
• Improves indoor humidity by 10% in the cold weather
• Less output in mild weather & higher humidity home
Pg. 39
Conclusions
• Cost effective over its lifetime
• The only alternative to a condensing furnace upgrade
• Likely the only way to achieve savings before we
(slowly) phase out the hundreds of thousands of I.D.
furnaces over the next 20 to 50 years
BUT
Pg. 40
CIP Recommendations
• GTI has yet to entice a manufacturer to take up the concept• Potentially cannibalize condensing furnace sales
• Cite risks associated with creating a new product without an established market
• What can we do? What can CIP do?• Direct rebate offerings for space heating and efficient humidification
savings
• Develop a retrofit program to kick-start a market. Secure a sufficient number of participants to justify TMH production
• Pursue public/private partnership to lower risks of commercialization (e.g Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) programs)
around securing a certain number of participants through a preprocess guaranteeing a sufficient quantity of TMH sales to a potential manufacturer, thus reducing the initial risk of commercialization.Lastly, the pursuit of a public/private partnership may sufficiently alleviate the risk of commercialization. The results of this study as well as prior work by GTI, may be sufficient to develop a partnership with a manufacturer to obtain public funding that facilitate commercialization. For example via the Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) programs.