Humidity Control: Tales From the Damp Side Michael Brown, ICF - - PowerPoint PPT Presentation

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Humidity Control: Tales From the Damp Side

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Michael Brown, ICF Frank Swol, EAM Associates February 25th, 2020

ICF proprietary and confidential. Do not copy, distribute, or disclose.

Agenda

▪Humidity Introduction ▪Suggestions and Best Practices ▪Humidity Models

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Humidity Introduction

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Humidity Basics

▪ Air Contains Water ▪ We measure with relative humidity (0-100%) ▪ Hot air can hold more water than cold air ▪ When you cool air down it loses water (condensation) ▪ Maine is cold! ▪ … and humid?!

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Example

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Humidity Basics Example

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• 40
• 35
• 30
• 25
• 20
• 15
• 10
• 5

Outdoors Indoors Humid Dry Bulb Temp (F)

• 6 °F

67 °F 67 °F Relative Humidity (%) 98 % 24 % 100 % Absolute Humidity (kg/kg) 0.0006 0.0033 0.0142 Cups of Water in my House 1 4 18

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Balancing Act: Moisture In – Moisture Out = Humidity

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Moisture In:

• Infiltration
• WH Ventilation
• Cooking
• Bathing
• Drying Bldg. Materials

Moisture Out:

• Air Conditioner
• Local Ventilation

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Why Do We Care About High Humidity?

▪ It’s uncomfortable! ▪ Excess moisture can lead to mold and other biological pollutants

▪ Health concerns (e.g., asthma, allergies) ▪ Building material decay

▪ Recommended < 60% RH

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Mold

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Efficient Homes & Humidity Control

▪ Efficient homes tend to decrease sensible load, but not latent load as much

▪ True with modern Code, HERS Rated, and ENERGY STAR homes!

▪ With relatively high latent loads, more likely to meet setpoint quickly, short cycle, and not dehumidify

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Sensible Load (temperature) Latent Load (moisture) Home Efficiency

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Equipment sizing and dehumidification

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Right-Sized AC Oversized AC ▪ Water condenses and drains away ▪ Takes time ▪ Not enough time ▪ ‘Short cycles’ ▪ Cools but doesn’t dehumidify

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Suggestions / Best Practices

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Humidity Control Research Low / No-Cost Solutions

▪ Mid-Atlantic builders in an ICF new homes EE program were having trouble with high humidity.

▪ Wanted to know about ventilation, and options before an expensive dehumidification system.

▪ Recommendations summarized in a white paper. ▪ Make sure you do these recommendations right before jumping to supplemental dehumidification.

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HVAC Solutions: Sizing

▪ ENERGY STAR HVAC Design Report & Rater Design Review Checklist ▪ Calculate accurate loads

▪ Use industry standard practices ▪ Ensure design = actual home

▪ Properly size equipment

▪ Enough sensible and latent capacity ▪ Limit oversizing!

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HVAC Solutions: Commissioning

▪ ENERGY STAR HVAC Commissioning Checklist ▪ Commission system to ensure equipment operates as designed

▪ Duct leakage ▪ Airflow ▪ Refrigerant Charge

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HVAC Solutions: Sensible Heat Ratio (SHR)

▪ Lower SHR = more latent capacity

▪ Pay attention to SHR when selecting equipment.

▪ SHR and latent capacity change with conditions, consider evaluating off peak conditions.

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2 4 6 8 10 12 70 75 80 85 90 95 100 105 110

Latent Capacity Outdoor Temperature

0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 70 75 80 85 90 95 100 105 110

SHR Outdoor Temperature

14 SEER 16 SEER Nominal Capacity (Tons) 3.0 3.0 SHR 0.75 0.82 Latent Capacity (kBtuh) 9.0 6.5

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HVAC Solutions: Supply Fan Overrun

▪ Supply fan overrun: HVAC fan runs for a short period after compressor turns off

▪ Provides a little extra cooling ▪ Increases SEER rating

▪ Adds moisture back to the living space. ▪ Disable supply fan overrun if you struggle with humidity control.

▪ 90 second fan overrun in Miami leads to 1,300 additional hours (53 days!) above 60% RH

http://publications.energyresearch.ucf.edu/wp-content/uploads/2018/06/FSEC-PF-443-08.pdf http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1716-07.pdf 15

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Ventilation Solutions: Local Mechanical Exhaust

▪ ENERGY STAR Rater Field Checklist ▪ Besides AC local exhaust is main way to remove moisture directly from the source ▪ Make sure to:

▪ Measure airflow rate ▪ Verify meets minimum rates ▪ Verify exhausts directly outdoors

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55 CFM

Outdoors

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Ventilation Solutions: Recommended Mechanical Ventilation Strategies

https://www.nrel.gov/docs/fy14osti/60675.pdf 17

Exhaust Supply Balanced (ERV)

Modeled hours above 60% RH

Hours

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Homeowner Education Solutions

▪ Educate homeowners on how their actions can impact humidity control:

▪ Use kitchen and bathroom ventilation, or use ventilation with humidistat controls ▪ A higher cooling setpoint will mean less dehumidification ▪ Set fan mode to “AUTO” not “ON”

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FAN ON AUTO

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Humidity Models

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ICF proprietary and confidential. Do not copy, distribute, or disclose.

When is there high humidity?

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200 400 J F M A M J J A S O N D

Month

(hours > 60% RH)

Outdoor Temp.

(hours > 60% RH)

ENERGY STAR v3.1 home modeled in Baltimore MD using BEopt

30 60 40 45 50 55 60 65 70 75 80 85 90 95 100

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Measure Humidity Savings

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ENERGY STAR v3.1 home modeled in Baltimore MD using BEopt

Humidity

(hours > 60% RH)

Baseline Bathroom Exhaust HPWH AC SHR WH Ventilation Total Impact

• ENERGY STAR

v3.1 in MD

• 964 hours (40 days)

humidity > 60% RH

• Modeled 2x the

shower load

• Minimal total space

impact, localized impact

• Heat pump water

heater in conditioned space

• Likely challenges

architecturally

• Improving from 0.82

to 0.73 sensible heat ratio

• Improving from

Exhaust to ERV

• Large impact
• 66% reduction

(27 days)

• Not cumulative due

to interactive effects

Humidity Reductions

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Ventilation Strategies

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$1,818 $1,874 $1,817 $1,813

Exhaust Supply Balanced (ERV) Balanced (HRV) Energy Cost Humidity

(hours > 60% RH) 964 724 889 444

ENERGY STAR v3.1 home modeled in Baltimore MD using BEopt

ICF proprietary and confidential. Do not copy, distribute, or disclose.

Investing in Efficiency / Humidity

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69 68 68 62 62

ERI Baseline Window Upgrade ERV 16 SEER AC Tankless DHW Incremental Measure Cost

$- $2,544 $247 $902 $1,284 571 591 522 603 246

Humidity

(hours > 60% RH)

~2012 IECC home modeled in Baltimore MD using BEopt

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Key Takeaway

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~2012 IECC home modeled in Baltimore MD using BEopt

▪ Consider humidity control when improving home efficiency

Case Study: Multi-Family Project

3-Story Low-Rise MF Building in Delaware

• Climate Zone 4 ( ~4 miles from coast)
• 2012 IECC construction
• Summer 2018
• Various units were experiencing high indoor

relative humidity ( >70%) and mold growth

• Mold located at door frames, walls, and on

absorbent materials (clothes, furniture, knickknacks)

• Field inspection and analysis determined a

series of fundamental design, product selection, and installation errors to be the causal factors

3-Story Low-Rise MF Building in Delaware

• Two disclaimers before we

continue: – NOT a HERS Rated or Energy Star project! – NOT designed or constructed with Rater’s involvement!

Heating & Cooling Equipment

• Engineer’s Sizing vs. Contractor’s Equipment

Selection – EAM QC Manual J

• “Unrelated” Value Engineering Forcing MEP Design

Changes – Return Ductwork Layout

• Engineer’s BOD Equipment Suitability to

Architectural Layout

• Return Airflow Pathways
• Contractor “Fixes” Following Appearance of Issues

Let the errors begin…

• Misread of equipment model

numbers – Plan: 1-ton AC (24k heating) – Installed: 2-ton AC (51k heating)

• Alteration of exterior balcony

– Fiberglass to Composite Decking

These aren’t the numbers you’re looking for…

These aren’t the numbers you’re looking for…

And this isn’t going to help either…

And this isn’t going to help either…

What happens in the home stays in the home…

No Kitchen Exhaust to Outside Average Bath Fan Flow = 16 CFM (as low as 10 CFM)

Implemented Solutions

• HVAC equipment swapped out
• Contractor “improvements” removed
• Mechanical closet insulation retained
• Tenant mechanical closet access removed
• Adequate return air pathway added between master

bedroom and living space

• Bath fans replaced with a higher static 80 CFM

model on delayed off switch

Implemented Solutions

• Facility management keeping dehumidifiers onsite

for spot use

• Tenant education (HVAC system operation, furniture

placement, interior door positioning)

• Had Rater’s engineering department redo the MEP

design for future buildings ☺

• How was Summer 2019?

Case Study: Single Family Project

You can meet code and above-code program requirements and still sometimes get ducts that do this:

2-Story Single Family Homes in New Jersey

• Climate Zone 4 (inland)
• Affordable Housing (24-units)
• (1) 2BR and (1) 3BR Floorplan (no options)
• Energy Star & LEED for Homes
• Summer 2018 & 2019
• R-21 2x6 construction with R6 insulated sheathing,

low-E/argon windows, and R-49 blown attic

2-Story Single Family Homes in New Jersey

• Exhaust-only ASHRAE 62.2 Whole House Ventilation
• Single Zone HVAC System (Variable speed gas furnace / Single

stage AC)

• All ductwork located in “conditioned space” (interstitial cavity

between 1st and 2nd floor)

• Ductwork was not insulated, and a number of homes began

exhibiting serious condensation issues sufficient to damage drywall & other building materials

Testing took place on an ideally representative day with a temperature range from 86-91⁰ and high solar gain from mostly sunny skies.

• 73⁰ thermostat setpoint
• 73⁰ thermostat indoor temp reading
• 50% RH dehumidifier setpoint
• 57% RH dehumidifier indoor RH reading
• 70.5⁰ in supply air floor cavity
• 62.2% RH in supply air floor cavity
• 61.1⁰ supply air at evaporator coil
• 71.7% RH supply air at evaporator coil

There was no condensation on the ductwork at this time. The thermostat was then lowered down to 70⁰ in order to drive the system towards worst case conditions.

Initial Conditions (as found at 11am)

At 12:30pm after ~30 minutes of operation the below readings were taken:

• Supply air temp at the evaporator coil was down to 60.3⁰
• Supply air RH at the evaporator coil was up to 82.9%
• Air temp in supply air floor cavity had dropped to 66.3⁰
• Air RH in supply air floor cavity had risen to 71.9%

The duct surface was now beginning to cover in a sheen of

• condensation. This is because the duct surface temperature in places

was now going below 56⁰ which was the dewpoint for the above air temp/RH conditions

1st Testing Interval

The AC system was run in this condition for another 1.5 hours, the home was revisited at 2pm:

• Room air temperature was now down to 72⁰ (thermostat set to 70⁰ still)
• Supply air temp at the evaporator coil was down to 59⁰
• Supply air RH at the evaporator coil was at 80.2%
• System was working well with a return air temp of 72⁰ and 60% RH
• The duct surface temperature was now down to 53.2⁰, well below the

dewpoint for the floor cavity air

At this point the ducts were now heavily sweating and in worst case condition so it was time to test the cavity ventilation solution

2nd Testing Interval

• 1. The system was working well for conditioning the home’s air, BUT the air in the

floor cavity was not participating in that process.

• 2. The air in the joists bays was over 10⁰ COLDER than the air in the home. At

those lows temps it can’t hold on to moisture. The uninsulated ducts are sub- cooling the cavity space.

• 3. In joist bays without ducts the air was essentially the same temp as inside the

living space.

• 4. All this added up to a general dew point in the cavity of 59⁰. This meant

anything colder would be a condensing surface, and duct surface temperatures were recorded below this temp in many locations, getting worse closer to the air handler

• 5. Conclusion was that we had to take steps to make the ducts warmer, and/or

to warm and dry the air around the ducts.

Initial Conclusions

At 2:30pm a Duct-blaster fan was installed at the passive air vent that had been cut into the laundry closet ceiling. It was set to deliver ~200 CFM into the floor/ceiling cavity.

• 50% (100 CFM) was determined via flow hood to be exiting the other

end of the HVAC soffit, the other 50% was being lost to leakage points in the cavity space.

• This was actually a good check for the tightness of the band joist

cavity, that amount of leakage was quite small at the test pressure of 25 Pascals. Most importantly air was transiting the soffit cavity and well dispersing in the space.

Interstitial Cavity Ventilation Test

At 4pm after 1.5 hours of ventilation operation the audit team returned to the home for the final time.

• Room air temperature was still at 72⁰ (thermostat set to 70⁰ still so

the AC had been running constantly during the entire test)

• The worst-case duct surface temp found was 57⁰, but was in most

places was much higher, up in the 60⁰ range

• The air temperature/RH in the floor-ceiling cavity was now 65⁰ and

64% RH The AC system had reached a solid steady state of supply air with a temp/RH of 57⁰/80% and a return air temp/RH of 71.5⁰/56.5%

Interstitial Cavity Ventilation Test

All condensation on the ducts was now gone. The air temp/RH in the cavity were now at a state where the dewpoint had been driven down to ~52⁰.

• It was impossible for condensation to occur now because even the

coldest air in the system back at the evaporator coil was 57⁰.

• This situation would have continued to improve with further run-

time. For purposes of this test the AC duct sweating was allowed to get out

• f control before the ventilation system was tested, in actual practice

the ventilation system will run in conjunction.

Interstitial Cavity Ventilation Test

• Thermostats locked out to 70⁰ as the minimum. Residents instructed

to use FAN AUTO setting only.

• Dehumidifier set to 45% RH.
• Cooling fan speed turned up (to raise supply air temp). Cooling fan

set to terminate operation with condenser cut-off. No supply fan

• verrun.
• Had to balance with living space humidity level concerns
• Cut back drywall ceiling around supply plenum above evaporator
• coil. Wrapped plenum with insulation extending slightly up into
• cavity. Sealed insulation outer vapor barrier to drywall with foam

sealant.

Final Implemented Measures

• Installed passive air grille at far end of HVAC soffit to allow for an

airflow pathway for the forced ventilation system.

• Installed floor/ceiling cavity mechanical ventilation system utilizing

HVAC relay control actuation.

• Residents educated on proper home setup during AC use. Windows,

exhaust fans, covering of supply/return registers with furniture, cleaning of dehumidifier filter, and replacement of HVAC filter.

Final Implemented Measures

What to consider if low-cost & low- impact measures don’t work

Advanced Options for Humidity & Condensation Control

Insulate ALL ductwork regardless of location

• Correctly sized systems run a lot
• Ducts are now highly sealed and do

not waste condition interstitial spaces Variable capacity AC equipment

• Better match sensible/latent load

ratios

• Limitations of 2-stage equipment

due to offered minimum sizing

Advanced Options for Humidity & Condensation Control

Keep the major component specifications in line with each other

• Don’t spend so much on one area that another must be

short-changed.

• The prime example for this moisture issue seems to be an

extremely well insulated shell coupled with single-stage AC equipment and exhaust-only ventilation.

VS

Advanced Options for Humidity & Condensation Control

Spray foam band joists

• This area is notoriously leaky. It also allows moist air to

infiltrate cavities that contain cold ducts. Builders using this detail have experienced fewer duct sweating/drywall damage issues.

Advanced Options for Humidity & Condensation Control

HVAC System Design & Equipment

• Install zoned or multiple systems (aesthetics vs function)
• Leverage ductless HVAC systems & other technology
• Understand dedicated dehumidification systems may not be a

luxury item in your area anymore

• Don’t discount interior moisture sources and check you wiring!

Advanced Options for Moisture Control

Restrict cooling operation range

• System designers are constrained to certain cooling indoor and
• utdoor design conditions. Depending on the exact system

being used and other factors, it may not be possible to allow the homeowner/tenant to choose whatever cooling setpoint they wish, AND still have the system maintain appropriate levels of indoor relative humidity.

Advanced Options for Moisture Control

Construction Scheduling & Best Practices

• Initial conditions (rainfall during key

milestones)

• Location of unit within building for multi-

family (slab vs top-floor)

• Monitor sub-contractors during latter stages
• Check your deliveries, test your building, and

dehumidify DURING construction if needed

• Time of year for initial building occupation
• Use unfortunate problem events as
• pportunities to improve process on future

projects

Advanced Options for Moisture Control

PSA for Raters and HVAC Designers

• Get any proposed specifications which

are not executed or value engineering affecting this moisture space in writing!

• Make sure you know more about

available technology options than your clients do.

• Encourage your project teams to do

away with “or equivalent” for certain components.

• Find knowledgeable OEM

representatives to work with

Discussion / Q &A

• Do you specifically advise clients on humidity

control when considering measure for a house? – What’s your approach? What do you recommend?

• How many of you have heard complaints on high

humidity? – What did you do to address? – Was there a cause identified?

• What reasons are you given when people tell you

they can’t or don’t want to spend more money on better humidity control?

Discussion / Q &A

• Do you feel like there is pushback from those who don’t think

climate change is a real factor in these increasing moisture problems?

• Have you had success getting builders or homeowners buying

into the concept that ventilation and indoor air quality isn’t just some invisible thing no one cares about in comparison to something like the stereotypical granite countertops? If so how did you present that?

• Would you like to see above code programs do more with their

requirements to prevent builders from designing packages which have a high risk of humidity problems?

Contact Info

 Michael Brown

ICF

Email: Michael.Brown2@icf.com

 Frank Swol

EAM Associates

Email: fswol@eamenergy.com