Whole House Dehumidification for Energy Savings and Occupant

Whole House Dehumidification for Occupant Comfort and Energy Savings

June 2009

Research Products Corporation 1015 East Washington Avenue Madis on, WI 53703 www .aprilaire.com INTRODUCTION

The relative hum idity inside of a hom e or bu ilding, referred to as th e indoor RH, should be maintained below certa in levels f or the comf ort and health o f the occupants as well as f or the preserv ation of the building and its contents.

The indoor RH that is comfortable for hum ans varies from individual to individual and is dependent on tem perature and air curren ts (f rom fans and furnace blower). F or hum an comfort, during the cooling season, the indoor RH should not exceed 60%. Annoying insects such as earwigs and m illip edes in a hom e can be reduced or elim inated by reducing the indoo r RH with a dehum idif ier.

High indoor RH is associated with num erous hea lth issues for the occu pants. These include allergies, asthm a, arthritis, gout , infections and diseases from fungi and fungal toxins and m any others. Based on health issues it is recomm en ded that the indoor RH be m aintained below 60%.

High indoor RH increases the prob ability that the hom e or build ing and its contents m ay be dam aged. Corrosion, warping of wood, funga l (m ol d) growth and dam age from i nsects will occur if the indoor RH is high enough. Da mage to or m alfunction of the building structure, electronics (TV, com put ers, etc. ), medical de vic es (Eye Lasik, MRI sca nner, etc. ) furnitu re (som e m ay be antiques), other wood item s used in the construction of the hom e or building like floors and doors, m usical instrum ents (piano, violin, guitars, etc.), wall coatings (paint and wall paper), paper item s (books, periodicals, com ics, stam ps, art, etc. ) m ay occur and occur m ore rapidly with increasing RH. For preservation of the build ing a nd its contents it is recomm ended that indoor RH be maintained below 60%.

Therefore, based on comfort and health of the occupants as well as the preservation of the hom e or building and its cont ents, the indoor RH should be m aintained below 60%. Throughout this paper 60% will b e used as th e indoor RH by whi ch comfort, health and preserv ation of the hom e and it con tents will b e judged.

Conventional air cond itioning, the ty pe of air c ondition ing installed in most every hom e, cools the air as well as rem oving m oisture from the air and is the most frequently used equipm ent to reduce the indoor RH. Conventi onal air conditioning does not pr ovide control of indoor RH and does not m aintain the indoor RH at accepta ble levels througho ut the year because it operates based on indoor tem perature (sensible cooling load) and not on indoor RH (latent load). In no rthern clim ates, th ere is a sm all sens ible cooling load dur ing the m onths of May & June, September & October and at nights duri ng the summ er months (July & A ugust). In southern clim ates there is a sm all sensible cooling load from December throu gh March. Therefore, these m onths will prese nt the m ost challeng ing tim es in mainta ining a cceptab le indoor RH level at these locations.

If a dehum idifier is used in conjunction with air conditioning and opera ted properly, the indoor RH can be m aintained below 60% RH, while pr oviding a significant reduction in energy usage (energy savings). The purpose of this paper is to present so me operatio nal str ateg ies f or air conditioning and dehum idification system s th at provid e acceptable indoor RH levels and significant energy savings. METHODS

A residential hom e in Miam i, FL was sim ulated on an hourly basis with TRNSYS, a widely used building sim ulation program . The hom e is re ferred to as a “High Efficiency House” and is designed for a hot, hum id clim ate. This hom e is representative of a newly constructed air tight, energy efficient hom e as well as a condom inium .

The hom e has a slab-on-grade foundation, which is the predom inant foundation type in a hot hum id clim ate. The hom e has 4 be dr oom s, 8.0 foot high ceilings and 2000 ft 2 of conditioned floor area. The hom e is extrem ely energy effici ent and air tight. R-value s f or the walls, ceiling and floor are 19.4, 38.5, and 13.0 (hr-ft 2-°F)/Btu respectively. The m edian infiltration rate, based on a variable infiltration m odel, is 0.17 ach. There is no supplem ental m echanical ventilation.

Peak and average occupancy rate for the hom e is 3.0 and 2.4 people. Th e Internal Moisture Gain from hum an occupation is 10.3 pounds daily and is on a fixed schedule. An addition al, variable amount of m oistu re that contributes to the Internal Moisture G ain is included in the model and is from re-evaporatio n off the air conditioning coil . Moisture capacitance of building m aterials and the contents of the hom e is included in the m odel.

The capacity of the air conditione r in the hom e is 1.7 tons with an Energy Efficiency Ratio, EER, of 13.3 (Btu/hr) /watt withou t the HVAC fan and a Se asonal Energy Efficiency Ratio, SEER, of 13 (Btu/hr)/watt. The sam e air conditioner is used in the conventional air conditioning system and in the air condition ing and dehum idification sy stem . The sm all size of the air co ndition er, 1. 7 tons, is a r esult of th e hom e being extrem ely e nergy ef ficie nt and a ir tight. The HVAC system fan uses 0.18 watts/cfm , delivers 680 cfm a nd operates only when cooling is required. The dehum idifier has an integral fan and operate s only when the indoor RH exceeds the RH set point and ha s a rated capacity of 90 pints /day. Intern al sen sible heat gains include fixed schedule lighting and othe r equipm ent in the hom e (5,635 kW h annually), as well as an am ount from the dehum idif ier that depends on indoor conditions.

RESULTS

STRATEG Y 1: Cooling Set Point

A num ber of factors affect th e therm al comfor t of the occupants of a hom e or building and include air tem perature, air cu rren ts and hum idity. Occupants experience equivalent com fort at higher tem peratu res wh en the indo or RH is lowered. ASHRAE incorporates th is concept in the com fort zone in A SHRAE Sta ndard 55-2004 , Thermal Environ mental Conditions f or Hum an Occ upancy. A published report indicates that schools served by a dehum idification system were m aintained warm er than schools se rved by a conventional ai r conditioning system with equivalent occupant comfort.

In this study, the perform ance of a conventio nal air conditioning system with a temperature setting (set point) of 75.0 °F was compared to an air conditioning and dehum idification system with set points of 78.0 °F and 59% RH. The diffe rence in the cooling set point in this study is 3.0 °F. The 59% set point for the dehum idifier was chosen to keep the indoor RH below 60%. Hourly indoor Figure 1. I ndoor RH vs Ho ur of Ye ar f or Strategy 1 RH values for 80 Strategy 1 were Annu al Hour s > 6 0% RH 75 AC S ystem: 1,641 ho urs ( 18.7% ) predicted using AC & D H S ystem: 0 h ours ( 0%) the m odel and are shown in F igure 70 1. The 65 dehum idif ier operates 60 prim arily f rom Decem ber I 55 n through March d o o when the s ensible r 50 R cooling loa d is H

sm allest; the % 45 conventional air Jan Feb Mar Apr May Jun Jul Aug Se pOctNovDec conditioning 40 system only 0100 0 2000 3000 400 0 5000 600 07000 80 00 900 0 operates 122 Hou r o f Y ear hours during these 4 m onths. The dehum idifier has a dram atic im pact on the indoor R H during this tim e by maintaining the indoor RH below 60% at all tim es. In January, the indoor RH with conventional air conditioning exceeds 60% fo r 506 hours (68.0 % of t he m onth) and 70% for 71 hours (9.5% of the month). On an annual basis the indoor RH with conventional air conditioning exceeds 60% for 1,641 hours (18.7 % of the year). Therefore, this con ventional air conditioning system provides ve ry poor control of the indoor RH. The air conditioning and dehum idif ication system m aintains e xcellent con tro l; the ind oor RH is below 60% at all tim es throughout the year.

Fi gur e 2 . T otal Energy Us age v s M onth f or Strategy 1 60 0

Total E ner gy Usage 52 4 52 1 AC Sy stem: 3 ,417 kW 50 0 AC & D H Sy stem : 2 ,808 kW

427 41 9 40 6 401 Monthly energy 40 0 usage for these 34 3 32 0 two system s is 31 3 314 30 0 27 4 shown in Figure r g

y 24 1 2. Energy 23 0 22 1 U s savings occur a 17 8 g 20 0 173

e 15 8 from April T 142 13 8 o

k 12 7 t W through a 11 0 11 3 l Novem ber as a E 10 0 81 n result of the 3.0 e 52 °F higher cooling set point 0 for the air Ja n FebMarAprMayJun Ju l Aug Sep Oct Nov Dec conditioning and Mo nth dehum idification system . Table 1 provides an annual Tabl e 1 com parison of the Annu al Perfo rmanc e S ummary fo rStra tegy 1 conventional air conditioning system and the air Perf orm anc e Air C ondit io ning Conventio nal conditioning and Pa ramater & D ehumidifier Ai r C onditioning dehum idification system for Strategy 1. The air En er gy U sage, k Wh 2, 80 83,417 conditioning and % E nergy S avings 18 NA dehum idification system 1279 (A C) Operation T ime, ho urs 19 11 provides an annual energy x25 8 (D H) savings of 18% as compared Time > 60% RH , ho urs 01 ,641 to the conventional air % T ime > 6 0% R H 01 8.7 conditioning system . The air conditioning and dehum idificati on system m aintains the indoor RH below 60% throughout the year while the conventional air con dition ing sy stem allows the ind oor RH to exceed 60% for 1,641 hours (18.7% of the year).

Therefore, s ignifican t energy savin gs and comf ort im provem ents occur when using an air conditioning and dehum idification system at a slightly higher cooling set point.

STRATEG Y 2: Overcooling

One practice that is often em ploye d to im prove th e comf ort leve l in a hom e or building is to significan tly lower th e tem perature setting (s et point) for the conventional air con dition ing system . Thi s is referred to as overcooli ng. Overcooling improves comfort by reducing both the indoor temperature and the indoor RH. Overcooling is fre quently em ployed even though it consum es a significant amount of energy and m ay result in moisture and mold problem s if the cooling set point is lower than the dew point of the outdoor air.

In this study, the perform ance of a conventional air conditioning system operating at a set point of 72.0 °F (overcooling) was Figu re 3. Indoor R H v s H our of Year for Strategy 2 com pared to an 80 air conditioning Annu al H our s > 60% RH and 75 AC :280 h ours ( 3.2%) dehum idification AC & D H: 0 h ours (0%) system with set 70 points of 78.0 °F and 59% (the 65 sam e system from 60 Strategy 1). 55 I n

Hourly indoor d o

RH values for o r 50 Strategy 2 were R H predic ted using 45 % the m odel and are Jan Feb Ma rAprMa y Jun Jul Aug Sep Oc tNovDe c shown in Figure 40 3. 0 100 02000300 04000500 0 6000 7000 8000 9000 Hour of Year

5 The conventional air co ndition ing s ystem opera tes 390 hours from December to March, m ore than thr ee tim es as much as the con ventiona l ai r condition ing in Strateg y 1, yet in J anuary, the indoor RH with conven tional air condition ing exceeds 60 % for 115 hours (15.5 % of the month). On an annual basis th e indoor RH with c onventional air conditio ning exceeds 60% for 280 hours (3.2 % of the year). The air conditi oning and dehum idifier system m aintains the indoor RH below 60% at all tim es throughout the year.

Monthly energy Figure 4. T ota lEnergyUsage v s. Month fo r S trate gy 2 usage for these 700 64 9 two system s is Total E nergy Usage 64 3 shown in Figure AC S ystem :4,973 kW 600 4. Energy AC & DH S ystem: 2 ,808 kW 54 1 53 3 savings occur

W 500 every m onth of k 45 4 the year as a e 422 g 406 40 1 a result of the 6.0 s 400 U 347 °F higher y 33 9 g 32 0 31 3 r cooling set point e 28 6 282 n 300 27 4 26 7 for the E

l 24 1

a 22 1 conventional air t 21 0 o

T 200 conditioning 15 8 14 2 13 8 system . 11 3 100 81 Table 2 provides an annual 0 com parison of Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec the conventional air conditioning Mo nth system and the air conditioning and Tabl e2 dehum idification system for Annua l P erform ance S ummary for Strategy 2 Strategy 2. The air conditioning and Perf orm anc e Air Cond itioning Conventio nal dehum idification system Pa ramater & D ehu midi fi er Air C onditi onin g provides an annual energy savings of 44% as compared Energy U sag e, kWh 2,80 84,9 73 to the conventional air % E nergy S aving s 44 NA conditioning system . The air 1279 (A C) Operation T ime, ho urs 2757 conditioning and x25 8 (D H) dehum idification system Time > 60% RH , hours 0 280 maintains the indoor RH % T ime > 6 0% R H 03 .2 below 60% throughout the year while the conventional air condition ing system a llows the in door RH to exceed 60% for 280 hours (3.2% of the year). This conven tional air co ndition ing s trategy prov ides for better indoor RH levels an d com for t than tha t in Strategy 1, b ut it is s til l inadequate in January and February.

Therefore, v ery sign ificant energy savings as well as com fort im prove ments occur when using an air conditioning and dehum idification system ra ther than overcooling. In addition, the risk of da maging the hom e fr om m old problem s associ ated with overcooling has been elim inated. STRATEG Y 3: Unoccupied in Summer Months

In the US, about one in four retiree “snowbirds” (about 900,000 pe ople) reside in Florida to escape cold, northern clim ates during the winter. This seasonal occupancy creates a need for strategies for controlling th e indoor RH to avoid m old pr oblem s while m ini mizing energy usage when the hom e is unoccupied. Previous studi es have indicated that raising the set point of a conventional air co ndition ing s ystem to 83.0 to 85.0 ° F during th e unoccupied period reduces energy usage but does not provi de sufficient indoor RH control.

In this study, the perform ance of a conventiona l air conditioning system with a set point of 78.0 °F throughout the year was compared to an air conditioning and de hum idification system with set points of Figu re 5. Indoor RH vs Ho ur o fYear for S trategy 3 78.0 °F when 80 occupied Annual H our s > 60 %RH (Novem ber 75 AC: 258 1hours ( 29.5% ) through April), AC & DH: 0 h ours ( 0%) and 85.0 °F when 70 unoccupied (May

through October) % 65

and 59% RH H

R 60 year-round. r o o d n Hourly indoor I 55 RH values for Strategy 3 were 50 predicted using the m odel and are 45 Jan Feb Mar Ap r Ma yJun Jul Aug Se pOctNovDec shown in Figure 5. In January 40 with 0 1000 2000 300 0400 0500 0 6000 7000 800 09000 conventional air Ho ur of Year conditioning, the indoor RH exceeds Fi gure 6 . T otal En er gy Us age v s M onth fo r St rate gy 3 60% for 596 hours 60 0 (80.1%) and 70% Total E nerg y U sage AC S ystem: 2, 525 k W for 309 hours 50 0 (41.5%). AC & DH S ystem: 1 ,447 kW Therefore, this 40 6 402 conventional air 40 0 conditioning 317 31 3 system provides 30 0 274 very poor control 237 of the indoor RH. 203 216 20 0 158 14 2 138 Monthly energy T 13 5 126 126 o 10 3 11 3 t a 10 0 81 89 89 81 usage for these two l 65 68 66 E system s is shown n 24 e r in Figure 6. g

y 0 U

s Ja nFebMarApr May Jun Jul Aug Sep Oct Nov Dec a g e Mo nth k W Energy savings for the air conditioning and dehum idification system occur during the unoccupied period from May through October.

Table 3 provides an annual Tabl e3 com parison of the Annua l P erform ance S ummary for Strategy 3 conventional air conditioning system and the air Perf orm anc e Air Cond itioning Conventio nal conditioning and Pa ramater & D ehu midi fi er Air C onditi onin g dehum idification system for Strategy 3. The air Energy U sag e, kWh 1,44 72,5 25 conditioning and % E nergy S aving s 43 NA dehum idification system 414 (A C) Operation T ime, ho urs 1245 operates 201 and 252 hours, 35 4 (D H) respectively, annually when Time > 60% RH , hours 02 ,581 the hom e is occupied and 213 % T ime > 6 0% R H 02 9.5 and 102 hours, respectively, when unoccupied. The conventional air conditioning operates 1,076 hour s when occupied and 169 hours when unoccupied. The air condition ing and dehum idification system provides an annual energ y savings of 43% as com pared to the conventi onal air condition ing system . The air con dition ing and dehum idification system m aintains the i ndoor RH below 60% throughout the year while the conventional air con dition ing sy stem allows the indoor R H to exceed 60% for 2,581 hour s (29.5%).

Therefore, in seasonally occupied hom es ve ry significant energy savings and com fort im prove ments occur when using an air conditioni ng and dehum idification system rather than a conventional air conditioning system .

DISCUSS ION

This study c lear ly indica tes that the re are ope ra tional strateg ies in which an a ir cond ition ing and dehum idification system can be used to prov ide significant energy savings as compared to a conventio nal air cond ition ing system , while si gnifican tly im proving com fort and health of the occupan ts as well as preserv ation of the building and its contents.

Sim ilar results would be found in other hum id locations along the gulf coast and in the south such as Houston, TX and Jacksonville, FL si nce the cooling and dehum idification loads are sim ilar. Increasing the air exchang e rate from ventilation or looser co nstruc tion inc reases the num ber of hours the in door RH is greater th an 60% with the conventional air con dition ing system , m aking a dehum idifier even m ore be neficial. Sim ulations done in less hum id Midwestern locations indicate an air conditioning and dehu midification system can provide bette r com fort with sim ila r ene rgy usage and in som e cases an energy savings. Other energy and cost saving strategies fo r th e air cond itio ni ng and dehum idification system could be em ployed when the hom e is unoccupied such as running the dehum idifier during off peak hours. The best tim e of day for the dehum idifier to run is based on the size and air tightness of the hom e.