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Field Trials of a Waterless Home Heatingand Humidification Technology

Dexin Wang, PhD Shawn Scott Ainan Bao, PhD William Liss

ABSTRACT

It is generally accepted, and has been confirmed by studies, that humidification of dry indoor air to raise relative humidity (RH) during the heating

season is beneficial to the comfort and health of building occupants. Humidification also prevents adverse effects on wood floors and furniture and

reduces static electricity buildup which can harm electronic equipment.

Currently, the most widely used residential humidification technologies are forced air furnace mounted bypass wetted media, spray mist, and steam

humidifiers. These use city water as a water source and require additional furnace heat or electricity to evaporate the water, which consumes 4% or

more of the furnace fuel input. Mineral deposition, white dust and microbial growth problems are associated with these humidifiers. For

commercial building humidification, demineralized water is typically used for humidification equipment such as steam heat exchangers, electric and

ultrasonic humidifiers, compressed air atomizers, and high pressure cold water foggers. In addition to the energy consumption for the water

evaporation, energy is also needed to produce high-quality demineralized water through a reverse osmosis process.

A Transport Membrane Humidifier (TMH) technology was developed by using nanoporous membrane capillary condensation separation

mechanism to transport water vapor only from furnace combustion flue gas to humidify building air. After proving the technology in a laboratory

environment for an equivalent 4-year operation, two TMH units were installed for two home furnaces with AFUE ratings of 80%. The two

furnaces are from two different manufacturers with different ductwork configurations and different heating capacities, so two separate designs weremade to accommodate the difference. Both TMH units had been in operation through the 2010-2011 and 2011-2012 heating seasons in

Chicago area homes, and provided satisfactory whole house humidification with both occupied homes maintained at 40 to 60% RH. At the same

time, they boosted the two furnaces efficiency from around 80% to more than 95%, providing significant energy savings. Compared with

conventional whole house humidification technology, the TMH humidification benefit comes with no water connection, no need to change

filters/wetting pads/drums, no white dust to rooms, and no bacteria growth concerns from standing water. In addition no maintenance is required

for the TMH units.

INTRODUCTION

It is generally accepted, and has been confirmed by studies, that humidification of dry indoor air to raise relative

humidity (RH) during the heating season is beneficial to the comfort and health of building occupants. There are also

significant energy savings possible due to the apparent temperature phenomenon that allows people to feel more

comfortable (i.e., warmer) at higher RH. Humidification also prevents adverse effects on wood floors and furniture and

reduces static electricity buildup which can harm electronic equipment. ASHRAE Standard 62-1989, states, relative

humidity in habitable space preferable should be maintained between 30% and 60%... to minimize growth of allergenic and

pathogenic organisms. Notably, the lack of proper space humidification enhances the rate of influenza virus, resulting in a

significant number of illnesses and deaths each year. Humidity control is important in commercial buildings including

hospitals as well as many industrial processes, such as electronic and semiconductor manufacturing, medical supply,

SA-12-C006

42 ASHRAE Transactions

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printing application, woodworking and storage, and textile industries.

Currently, the most widely used residential humidification technologies are forced air furnace-mounted bypass wetted

media, spray mist, and steam humidifiers. These use city water as a water source and require additional furnace heat or

electricity to evaporate the water. Mineral deposition, white dust and microbial growth problems are associated with most

of these humidifiers. For commercial building humidification, demineralized water is typically used for humidification

equipment like steam heat exchangers, electric and ultrasonic humidifiers, compressed air atomizers, and high pressure cold

water foggers. In addition to the energy consumption for the water evaporation, energy is also needed to produce high-

quality demineralized water through a reverse osmosis process.

The Transport Membrane Humidifier (TMH) technology was developed by using a nanoporous membrane that

facilitates a capillary condensation separation mechanism which transports water vapor only from furnace combustion flue

gas to humidify building air. The capillary condensation action enables high water transport rates while also blocking non-

condensible gases from transporting across the membrane.

There are other research efforts aimed at using membranes to separate and transport water vapor for gas stream

dehydration, humidity control, and energy recovery in commercial HVAC systems. None of these applications, however,

has attempted to extract water vapor from a flue gas stream to humidify air. For all these and similar applications, only very

small trans-membrane total pressure is available. The driving force for water vapor to transport from one side of the

membrane to the other side relies mainly on the water vapor partial pressure difference between the two gas streams. For all

these reported applications, they are dealing with transporting moisture from a high humidity air stream to a low humidity

air stream, the water partial pressure difference is relatively small, less than 0.4 psi (2,760 pascal).

A flue gas stream typically has a dew point of 120 to 136F (49 to 58C) . This high temperature high humidity level

can create a greater than 2 psi (13,800 pascal) water vapor partial pressure difference with the circulating room air, which

usually has a dew point of 50F (10C) or lower. Using flue gas moisture to humidify the room air can provide five times

larger driving force across the membrane, therefore substantially less membrane surface area is needed. The reduced surface

area greatly lowers the cost and improves the prospect for a cost effective commercial application using the TMH. In

addition, since the flue gas is typically at much higher temperature (over 250F, or 121C), the TMH functions as a heat

exchanger to preheat the air stream to save energy.

The combined energy saving and humidification function with no potable water consumption makes this technologyunique. The reduced membrane surface area and simple design make it promising for a commercial product. To our

knowledge, no practical technology has ever been developed for humidifying room air with flue gas moisture for residential

use. TMH technology can reduce fuel use, eliminate city water consumption, completely avoid mineral deposition and white

dust, and avoid microbial growth, improving both the physical and financial health of the homeowners.

The TMH technology has been developed from concept to laboratory prototype, and the laboratory prototype TMH

has been tested and proved working well in a wide operation range for a residential furnace to add moisture into the

circulation air and enhance the mid-efficiency residential furnaces (around 80% AFUE) by about 15%. A long term testing

has also been carried out for this laboratory TMH for about 5,000 hour furnace operating time, which is equivalent to about

4 year operation time of a typical furnace. At the end of the testing period, the furnace efficency still can be enhanced by

13% from its baseline condition, with 5.0 lb/hr (2.27 kg/hr) moisture transport rate to the air, enough for home

humidification.

This paper will mainly introduce two actual home TMH installations and the test results, to show the TMH

technology real world performance on both whole house humidification effect and furnace efficiency enhancement in the

two occupied homes.

FIELD TRIAL DESIGN AND HOME INSTALLATION

TMH Installation Arrangement And System Setup

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As shown in Figure 1 a), the TMH is installed in the furnace air inlet ductwork. Inside the TMH, flue gas flows from

the membrane feed side, while the room circulating air that requires heating and humidification flows on the permeate side.

The low-temperature, high-flow-rate room circulating air passing over the membrane surfaces provides adequate membrane

cooling to facilitate the high-performance capillary condensation water vapor separation mode. Water from the flue gas is

transported to the air side, simultaneously heating and humidifying the air.

Figure 1: a) TMH install arrangement for a residential mid-efficiency furnace, b) P&ID for the TMH field trial installation

Detailed P&ID of the TMH installations with all the measurement is shown in Figure 1 b). The furnace natural gas

flow rate was measured by a natural gas flow meter. The furnace flue gas temperature, TMH air inlet/outlet temperatures,

and furnace air delivery temperature were measured by thermocouples. The air inlet and outlet dew points were measured

by hygrometers. An ID fan was installed to overcome the flue gas pressure drop through the TMH, and its electrical usage

was measured by a power meter. All experimental data were collected by a data acquisition system for post-processing.

TMH Module Assembly And Field Installation

Two occupied single family homes were selected to demonstrate the whole house TMH heat recovery and

humidification technology for residential furnaces, to verify their real world performance on furnace efficiency

improvement and whole house humidification.

Based on the laboratory prototype TMH design and assembling experience, two TMH modules with even lower air

and flue gas pressure drops were designed, and the two TMH module overall dimensions were based on the corresponding

furnace air ductwork cross sections and their fuel input capacities. Figure 2 c) shows pictures of the two TMH modules

built for the two field trail installations.

Pictures for the two TMH home installations are shown in Figure 2 a) and b). Furnace in home 1 has a 110,000

BTU/hr (3.22 kW) fuel input, furnace in home 2 has a 90,000 BTU/hr (2.63 kW) fuel input, both are mid-efficiencyfurnaces with AFUE rated 80%. The TMH modules were installed into the return air ductwork going into the furnaces, and

the flue gas heat and water were simultaneously recovered in the TMH and distributed into the homes after being further

heated by the furnaces. The flue gas side pressure drops through the TMH were measured as, 0.35-0.4 inches of water (87-

99 pascal) for home 1 TMH module, and 0.2-0.25 inches of water (50-62 pascal) for home 2.


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Figure 2: TMH installations for Home 1 a) (left) and Home 2 b) (middle), and the assembled TMH modules for Home 1 c)(right, top) and Home 2 c)(right, bottom)

TMH FIELD TRIAL RESULTS

Overall Furnace Efficiency Enhancement And Whole House Humidification Effect

The furnace overall efficiency is calculated based on the fuel higher heating value (HHV) and the furnace exhaust flue

gas temperature and moisture content. For both mid-efficiency furnaces with the TMH installations, the flue gas exhaust

temperatures decrease significantly from around 350F (177C) to around 105F (41C) for Home 1, and to around

95F(35C) for Home 2. Flue gas outlet dew points decrease from around 125F (52C) to around 90F(32C) for both

cases, and the furnace overall efficiencies thus increase significantly based on these lower flue gas outlet temperatures and

dew points. Calculation results show that the home 1 furnace efficiency increases from 81.5% without the TMH to 95.5%

with the TMH, and the home 2 furnace efficiency increases from 80.6% to 96.9%. The average moisture transport rates are

2.7-6.2 gallon per day (10-23 L per day) for home 1, and 1.5-4.8 gallon per day (5.7-18 L per day) for home 2, depending on

different room air temperatures and dew point conditions. Humidity levels for both homes have been maintained in a

comfortable range of 40-55% relative humidity with the TMH in operations.

For both homes, we have selected some days to operate the furnaces under TMH bypass mode to check the baseline

conditions without the TMHs. The results proved a significant humidity increase with the TMH in operation. For example,

relative humidity for Home 1 was 33-38% under TMH bypass mode, and 40-50% under TMH mode. Figure 3 shows the

humidification effect with and without the TMH operation in January, 2011 for Home 1. This figure shows the temperature

and relative humidity in the first and second floors for Home 1. Figure 4 shows similar conditions for Home 2, which is a

one-story single family home, with temperature and humidity loggers placed in its family room (FR) and living room (LR).

Detailed Furnace Performance With The TMH

Different furnaces have different operating characteristics, which is related to the furnace capacity, the heating area

size, and the customized thermostat programming. The mid-efficiency furnace for Home 1 has shorter heating cycles; and

the furnace for Home 2 has longer heating cycles.

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Figure 3: Home 1 room temperature and humidity with and without TMH in operation in January 2011

Figure 4: Home 2 room temperature and humidity with and without TMH in operation in January 2011

Figures 5 and 6 show the furnace characteristic temperatures, such as flue gas outlet temperature and dew point,

TMH air inlet and outlet temperatures and dew points, and the furnace final air delivery temperature, in a typical furnace

operation cycle for both homes, under the TMH mode and TMH bypass mode. From Figure 5, we can see the circulating

air dew point (Td) increases about 3

F(1.7

C) after it passes through the TMH module in the TMH mode in one heatingcycle, but has no change when the TMH was bypassed. For Home 2 as shown in Figure 6, the heating cycle is much

longer, and there is no obvious difference between the TMH inlet and outlet air dew points, but at the end of the heating

cycle, we can see the air dew point increased about 15F (8.3C) with the TMH, but only increased about 11F(6.1C) and

stayed at a lower level when the TMH is bypassed.

Figure 7 shows the instantaneous efficiency of one typical heating cycle for the two home furnaces at TMH bypass

mode and TMH mode. Averaged efficiency increases for these two typical heating cycles are from about 82% to 96% for

Home 1 furnace and 81% to 96% for Home 2 furnace.

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FRTempLRTempFRRHLRRH

Bypassmode VacationVacation


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Figure 5: Home 1 Furnace and TMH characteristic temperatures for a short heating cycle

Figure 6: Home 2 Furnace and TMH characteristic temperatures for a long heating cycle

Figure 7: Home 1 (left) and Home 2 (right) furnace instantaneous efficiency under TMH bypass mode and TMH mode forone heating cycle

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Economic Analysis and Potential Markets

There are about 35 million gas furnaces currently operating in U.S. homes. In 1998, 12% of furnaces available in the

market are considered high efficiency furnaces, and by 2010 high efficiency furnaces represented about 30% of national

furnace shipments. So it is estimated now more than 70% of furnaces in use are still mid efficiency furnaces (Federal

requirement for minimum 78% AFUE, most of them are around 80% AFUE). This TMH technology is first targeted forthis huge retrofit market to significantly boost the mid-efficiency furnace efficiency while at the same time providing whole

house humidification without external water consumption and other health benefits. The high efficiency furnace shipment

percentage is not expected to increase significantly in the near future considering various federal and state high efficiency

rebates are winding down, and the payback period is less attractive to customers for the much higher equipment cost of the

high efficiency furnaces, which are typically more than doubled of the mid efficiency furnace price. Although have not been

demonstrated yet, the TMH technology has already been further developed and proved in our laboratory to have the

potential to be used for high efficiency furnaces too. Many of the high efficiency furnaces have lower than 92% AFUE,

only a small amount of flue gas water vapor in these furnaces are condensed therefore the remaining water vapor is still

enough to humidify the homes, though the efficiency gain by the TMH installation will be lower for these furnaces. For

much higher efficiency furnaces, the TMH modules can be built into the furnaces to replace their condensing heat transfer

modules, so all the flue gas water vapor is available for the home humidification. Table 1 summarizes how the TMH stacksup against main conventional humidifier types. Besides the energy and health benefits listed in the table, there is no wetting

medium needed to be replaced regularly during a heating season compared with conventional humidifiers, which typically

costs about $30/year. The payback period of the TMH installation for a mid efficiency furnace is estimated at less than 4

years.

Table 1. Comparison of Current Furnace Humidifier Types with Proposed TMH

Commercial types ProposedType Bypass

humidifierSteamhumidifier

Spray misthumidifier

TMH

Additional furnace fuelconsumption

4% 0 4% 0

Electricity usage 12 watts 1,400 watts Negligible 20 wattsMineral deposition Yes Yes Yes a No

"White dust" in home Medium Zero High ZeroMicrobial growthpotential

High None Very low Very low

Water consumption b 15 gal/day 15 gal/day 12 gal/day Zero

Equipment cost $150-$225 $525-$850 $160-$200 $400 c

a potential clogging of spray nozzle; also requires water filter.b assumes average 3 gal/day additional water throughput to control mineral deposits.c preliminary cost target.

CONCLUSION

Two field trail TMH units were designed and tested for two typical mid-efficiency residential furnaces in two occupied

single family homes. The real world operating results showed the TMH units are capable of transferring enough water

vapor from furnace flue gas to circulating room air for humidification, and enhancing furnace efficiency by about 15%. The

home room temeprature and humidity continous monitoring data indicates both homes have been humidified to a

comfortable humidity level (40 to 60% RH) with the benefits of no external water consumption, no white dust and no

baterial growth concerns. For the two heating season operation of the two TMH units, the technology was proved can

provide comfortable and healthy humidification for the home owners and also greatly increase their furnace efficiencies.


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The TMH technology will be first targeted for the existing furnace retrofit market, and further development is for emerging

high efficiency furnace market for both retrofit and new installations.

ACKNOWLEDGMENTS

This work was sponsored by the Utilization Technology Development NFP.

NOMENCLATURE

RH: relative humidity

HHV: Higher Heating Value

Td: dew point

REFERENCES

Sterling, E.M., Arundel, A., and Sterling, T.D. 1985. Criteria for Human Exposure to Humidity in Occupied Buildings.ASHRAE Transactions 91:611-622.

ASHRAE. 1989. ANSI/ASHRAE Standard 62.1989,Ventilation for Acceptable Indoor Air Quality. Atlanta: American

Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.ASHRAE. 1992. ASHRAE Standard 55.1992,Thermal Environmental Conditions for Human Occupacy. Atlanta: AmericanSociety of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Asaeda, M., L. Du and M. Ushijima. 1985. Feasibility study on dehumidification of air by thin porous alumina gelmembrane p472-478; Drying 85. R. Toei and A.S. Mujumkar, ed. Washington D.C.: Hemisphere Publishing Corp.

Ray, R., D. D. Newbold, S.B. McCray, and D. T. Frlesen. 1992. A novel membrane device for the removal of water vaporand water droplets from air. 22nd international conf. on environmental system, Seattle, Washington, SAE 921322.

Scovazzo, P., A. Hoehn, and P. Todd. 2000. Membrane Porosity and Hydrophilic Membrane-based DehumidificationPerformance. J. Membrane Science 167:217-225.

Scovazzo, P., J. Burgos, A. Hoehn, P. Todd. 1998. Hydrophilic Membrane-based Humidity Control. J. Membrane Science149:69-81.

Zhang, L. and Y. Jiang. 1999. Heat and Mass Transfer in a Membrane-based Energy Recovery Ventilator. J. MembraneScience 163:29-38.

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