ENERGY EFFICIENCY AND
MOISTURE CONTROL IN THE
REPORT TO THE
Meeting Design & Facilitation By
Report By Jeff A. Blair
This document is available in
alternate formats upon request to Dept. of Community Affairs, Codes &
Standards,
ENERGY
EFFICIENCY AND MOISTURE CONTROL IN THE
REPORT TO THE
As a result of an identified need, Chairman Rodriguez
announced to the Commission and members of the public that there will be a “Symposium
on Energy Efficiency and Humidity Control in Florida Homes”. The idea for the
Symposium derived from discussions at the Energy Code Work Group meetings,
primarily between the window manufacturers and air conditioner manufacturers.
The Workgroup process identified the need for a technical forum to discuss how
energy efficiency measures that effect "sensible heat" gains impact
air conditioning equipment's ability to control indoor humidity. Industry
stakeholder put this workshop together with the help of Commission staff. The
goal of the Symposium is to create a broader base of understanding on how
building envelope energy efficiency measures interact with air conditioning
systems so we can better plot a strategy to improve energy efficiency
while maintaining healthy indoor environments.
The “Symposium on Energy Efficiency and Humidity
Control in Florida Homes” was held on February 28, 2007 in
BACKGROUND
A major portion of the energy used to cool homes in
Energy used to cool homes is due to two factors. The “latent
heat load” due to condensation of water vapor and “sensible heat load” which
relates to changing the air temperature. Sensible heat from solar radiation and
hotter outdoor air temperature is transmitted through the ceilings, windows,
walls and floors and heats up the indoor air. Sensible load removal by the
air-conditioner results in cooling down the air. In dry climates like the US
Southwest and most of the West and
When establishing building energy conservation regulations for hot and humid climates special attention must be given to latent energy loads, both because they are a major component of energy use and because increasing efficiency by only controlling sensible heat loads can result in an imbalance that enhances mold and mildew and degrades indoor air quality.
The challenge the Commission faces in setting energy conservation regulations for buildings is how to maintain a balance of requirements that address sensible and latent loads and result in healthy indoor environments. The evolution of the Florida Energy Code has addressed this balance successfully by taking significant steps to control latent load when major steps were taken were taken to reduce sensible load. The first major change in criteria addressing sensible load increased wall and ceiling insulation requirements to R-19 and R-30, respectively, and reduced allowable sensible load due to solar heat gain through windows. The Code established concurrent latent load control through requirements for sealing the building envelope to limit humid outdoor and attic air from infiltrating indoors. The next major step in building efficiency came when federal law imposed higher minimum efficiency requirements on air-conditioners. The equipment designed to meet those standards sacrificed latent load capacity so the Florida Energy Code enhanced air distribution system sealing requirements and air-conditioning system sizing requirements. It followed with requirements to ensure balanced air pressure in homes to which limit the depressurization of spaces that drives humid outdoor air indoors. As the state refocuses on energy independence and potential contributions of conservation of energy use for building cooling, attention must be paid to addressing humidity control in parallel with the national efforts to improve energy efficiency through reduction of sensible loads.
The most recent change in standards to effect sensible heat loads is the federal regulations that increased minimum efficiency for air-conditioners from SEER 10.0 to 13.0. As with the first change to minimum efficiencies for the air-conditioners, there is concern that the new equipment may have marginal capability of maintaining healthy indoor humidity control. This is in part due to the new equipment itself but is also due to sloppy design and construction practice in the air-conditioning service industry. Two primary factors can combine with the reduced moisture removal capability of new equipment to increase the number of humidity control problems: the sizing and selection of air-conditioning equipment and air distribution (duct) systems. Both have been addressed by requirements in the Energy and Mechanical Codes but widespread failure to comply with and enforce those requirements often result in the potential for a significant increase in system failures and unhealthy homes.
Two factors led to the organization of the
Commission-sponsored symposium on energy efficiency and humidity control of
February 2007. First, the uncertainties regarding humidity control with current
construction practices and new air-conditioning equipment complying with
federal SEER standards. Second, the renewed interest in energy conservation by
the Florida Legislature and advocacy for national efficiency standards at the
Commission. The purpose of the symposium was to educate non-air-conditioning
professionals on the humidity control challenge and to identify actions that
can be taken and options that can be pursued to maintain humidity control and
healthy environments while enhancing energy conservation standards for
Symposium participants identified two major options to be pursued through several actions. The first, and potentially most difficult, is education of the air-conditioning service industry, homebuilders and consumers about the humidity control and indoor air quality problems resulting from equipment over-sizing and poor air distribution systems. The second is to work with equipment manufacturer’s research and development teams to develop design parameters for equipment that can reliably increase the latent load removal capacity of equipment. The three major manufacturers represented at the symposium committed to working on improved equipment. These two paths provide the Commission with opportunities to keep in balance, while advancing, the two primary policies of the State:, energy conservation and healthy indoor environments.
Simplified Description of Humidity Control by Air
Conditioning Systems:
Air- conditioners control indoor humidity by moving air across the indoor cooling coil where water vapor condenses on the coil’s fins. The water vapor condenses only while the fins in the cooling coil are at a temperature below the “dew-point temperature”. The colder the fins the greater the condensation rate and the more moisture is removed from the air.
Two factors in air-conditioner equipment performance have changed to achieve the SEER 13.0 efficiency ratings required by the federal government. Average operating temperatures over a run cycle have gone up (reducing moisture removal capacity) and fans run longer after the compressor shuts down in order to take advantage of all of the compressed refrigerant and the energy it took to compress it. Running fans after the compressor cuts off not only allows the cooling coil to go above the dew-point temperature (preventing so water vapor/moisture from being condensed out of the air) but also causes condensed water on the coil to be re-evaporated and pushed back into the living space.
How much water vapor is removed from the house during a run cycle depends on how long the system runs at a condition where the cooling coil is colder than the dew-point temperature of the indoor air. The greater the start-up and run-down portion of the total run cycle, the lower the water vapor/moisture removal capacity of a system. Multiple short cycles will have greater total start-up and run-down portions of the total run time than long runtime cycles. So short-cycling of air-conditioners results in less moisture being removed from the conditioned air.
Short cycling occurs when the equipment is oversized. The system is turned off and on based only on the indoor air temperature, which is driven by “sensible” heat gains. Conventional air-conditioning systems are not “load matching” though there are complex multiple compressor systems available that are staged to better match the different rates of heat gain into a home that occur at different times of day. Conventional systems are off-on, delivering all of their cooling capacity or none. Equipment capacity depends on outdoor and indoor conditions (the hotter it is outdoors the less the capacity), but it does not track the rate of heat gain into a home--so it is not “load matching”. In operation, the thermostat (which senses are temperature and not moisture content), allows the temperature in the house to rise a set number of degrees above the temperature control setting before turning on the system. This allows a sensible load to build up in the house like a charge in a battery. How quickly the heat load is removed by the air-conditioner depends on its capacity (it’s size, usually referred to as “tons”). Four ton systems cool the air in a shorter time than three ton systems and, therefore, have a shorter run cycle.
The objective of air-conditioning equipment sizing and selection is to match the equipment capacity to the worst condition likely to occur on regular basis. Typically, systems are designed for a condition that will be the worst to occur 97.5% of the time. This provides smaller capacities that match the normal daily loads as they change through the day and night in response to outdoor temperature and sunshine. Smaller capacities result in longer run times to remove the sensible loads. Longer run times mean more water vapor removal and lower indoor humidity. Oversizing results in shorter run times, less water vapor condensed out of the air, and higher indoor humidity.
When air-conditioning contractors oversize (typically because they want to avoid call backs), or home builders and home owners demand large capacity equipment (they think larger is better), short cycling will result and humidity control will be problematic.
A separate contributing factor to over design of systems is “hot spots” in homes. Hot spots and damp, musky spots result from improperly designed and installed duct systems, which do not deliver adequate conditioned air to those spots. The simple-minded solution is to increase the system size to provide more cooling. This in turn causes systems to be larger than the total design loads for the home and creates short cycling. Poor duct systems also cause indoor humidity control problems by not providing enough air movement or mixing. The delivery air is at a lower humidity and reduces the humidity in the home by mixing with higher humidity air. When the air quantities and velocities are reduced by constrictions in the duct system, spot humidity (typically in remote or closed rooms and closets) can rise, leaving a damp feeling and musky odors.
Oversized equipment and poor air distribution duct systems are ubiquitous in the industry today. These system design and installation errors, combined with reduced latent energy removal capacity of the new higher efficiency air-conditioners, create an increased risk of failure to obtain adequate control of indoor humidity. This, when combined with other water control failures in building structures, can result in mold, mildew and other biological contamination and degraded indoor air quality.
The Energy Forum was convened
at approximately at 8:00 AM.
DCA
Staff Present
Rick Dixon, Mo Madani, and Ann Stanton.
The question and answer session, issues discussion, and next
steps were facilitated by Jeff Blair from the Florida Conflict Resolution
Consortium at
Forum Objectives
The following objectives were outlined for the Forum:
ü To Identify the Relationship of Sensible Heat Load and Air Conditioning System Performance to Moisture Control In Florida Homes
ü To Discuss the Effect of Heat Gain Through Windows on Sensible Heat Loads
ü To Identify the Sensible and Latent Heat Removal Performance Characteristics of Current Air Conditioning Equipment and Control Strategies
ü To Identify the Capabilities of the Air Conditioning Service Industry to Implement Equipment Measures for Effective Moisture Control
ü To Assess the Potential Risk for Loss of Moisture Control When Major Reductions of Sensible Gains are Paired with Current Equipment
ü
To Identify Steps that Can be Taken to Reduce
the Potential Risk if It Is Significant
Presentations
The following presentations were made to Forum participants in order to frame the issues and provide technical information for developing recommendations to address the issues. The presentations were given on PowerPoint and are included as attachments in PDF format.
Moisture Control in
Florida Homes and Its Relationship to Sensible Heat Loads, Rob Vierra,
(Included as Attachment 1)
Engineering and
Manufacturing Latent Load Removal by Residential Air Conditioning Systems, Roy
Crawford, Trane Corporation
(Included as Attachment 2)
Field Application of
Advanced Residential Air Conditioning Systems, Greg Spencer,
(Included as Attachment 3)
Sales and Marketing
of Advanced Residential Air Conditioning Systems, Jeff Hoffman, Carrier
Corporation
(Included as Attachment 4)
Residential AC
Systems Service Industry Status and Competency to Implement Effective Equipment
Based Moisture Control Strategies, Bob Cochell, FRACCA
(Included as Attachment 5)
The Economics of
Energy Efficient Windows, R. Christopher Mathis, Mathis Consulting Company.
Define
Problem/Synopsize Potential Risk Factors and Identify Actions and Strategies to
Address the Risk Factors
At the conclusion of the presentations the six presenters served as a panel to answer questions, define the problem, identify issues that must be addressed, prioritize the issues/options, and to decide on next steps.
The panelists were:
Bob Cochell, Roy Crawford, Jeff Hoffman, Chris Mathis, Greg Spencer, and Rob Vierra.
Question/Answer and Public Comment Summary
Questions:
Peter Birkbeck, Icynene
A driver on humidity with modern type construction is how the occupants live. Our mission is to seal the envelope, especially attic. How can they properly account for the tightness of a building? Re: sizing of cooling & ventilation equipment.
Answers: (Bob) I understand that new parameters (in sizing calc) include tight, semi-tight, loose construction. Generally run with semi-tight. I’m encouraging builders to put in quieter bath fans, close to shower. The ACCA J value of 1200 – 1800 Btu is close to correct.
Get calls from homeowners who don’t have window treatment yet & the homes are hot. Know the sizing is close.
(Chris) Air leakage load is challenge. Need to measure it. Have techniques to measure. Justify values used in load calc. Get more involved in duct testing, blower door testing, air sealing, etc. When you get up into better glass, the issue of window treatments goes away.
Arlene Stewart, AZS Consultants. Are HVAC contractors against low SHGC windows?
(Bob) No. Get hold of CILB. Need mandated 2 hours training for every contractor. Think low E glass is excellent. Do we have units that can handle it? Yes, but costly. Would like a two year window to get HVAC contractors on board.
(Chris) Education is essential. Disagree with Bob on timeline. Technology is not new in US, just
Philip Fairey, FSEC. I see a small misconception. If we were to mandate a 0.4 SHGC, it would do nothing to change energy use overall because it is in the baseline.
Roger Sanders, Energy TAC. Have had discussions on this subject. Feel that no progress on energy conservation unless have good enforcement. Until we have directives from the contractors that they want to do it right, won’t accomplish anything. Need incentive. People need to care. It all boils down to dollars & cents.
(Chris) You’re absolutely right; if not inspected right won’t get results.
Tina Neace. HVAC Design. Have impact of improperly done Manual Js. Bob, were you talking HVAC contractors, or include building contractors. Can’t get actual facts about what’s going into the building. Building departments aren’t even looking for Manual J.
(Rob) Dennis had asked if the A/C had been downsized based on sizing calc. No, 4 ton units were put in both test houses.
Gary Griffin, B&I Contractors, FBC. In terms of understanding issue of low E glass, if settle on 0.4 SHGC glass, value of glass on different orientations needs to be brought into the equation. Second issue: Want to see higher efficiency products and change without causing problems. It should be at a pace that will not create sick buildings. Do we need the code to define whether we have a problem?
(Chris) There is 0 correlation between sick buildings and low SHGC glass. In 1997, IECC & ASHRAE adopted 0.4 SHGC. RE orientation: Trouble is that without low SHGC glass, not just a west-facing issue.
(Rob) Benefit when spending limited dollars does differ. Cost benefit is small in some cases. Performance code puts in % glass. With tightening of the code and lower cost of windows, seeing more efficient windows going in.
Rick Dixon, FL DCA. When planning for more energy efficient buildings, we have taken steps to keep [avoid?] major shock in code. Need to solve issue with HVAC industry to insure more energy efficient buildings in future. Real problem is that majority of industry is not there. Mother’s home new a/c. Very bad practices seen.
Arlene Stewart: Have heard hard to get information from builders. Have heard that windows drive the load. Know that 0.4 SHGC not currently being used. If we did have a cap of some sort, would it make education, stocking, planning easier. Takes guesswork out of picture. No longer becomes high cost.
(Bob) Point is well taken. Would like to see timeline to get contractors to where they need to be.
(Jeff) Agree that education is the key to the whole thing. Company is selective on who they sell equipment to. Not all competitors take this position. Speaking to Manual J: can get any answer I want. Design criteria has to be done right.
Arlene Stewart: Need to simplify things. Education is not an easy thing to do. Manual J may be the more important calculation to focus on.
Pete Quintela: Building a better building is all about. Code does not state who enforces the energy code. Often done by Mechanical plans examiner & inspector—who are not certified to inspect feature that they are not trained to inspect. Much more involved. This is beyond the scope of his license. Need to catch the mouse, need better mousetrap.
Jim Larson, Cardinal Glass Industries. Discussion of windows being the culprit. Not just windows. Nothing to limit load calculation oversizing…need to prove the load. Simple limit that must be disproved.
(Rob) National scope trying to take gamesmanship out of the equation.
(Philip Fairey) You can get any number out of Manual J that you want. Doesn’t mean done correctly. National HERS specify how Man. J is used: interior temperature conditions, % design conditions, bathroom vent fans. Need standard for how it is done.
Identification of Key Issues and Prioritization Exercise
The facilitator, Jeff Blair, asked the panelists to identify
what they believed to be the key issues that should be addressed in order to
consider energy efficiency and moisture control in the
RANKING SCALE
5 Highest Level of
Priority; Urgent
4 High Priority
3 Moderate Level of
Priority
2 Low Level of Priority
1 Lowest Possible Priority; Group Should not Pursue
|
|
ISSUE |
RANK
|
5 |
4 |
3 |
2 |
1 |
RAW SCORE |
|
|
Proper design considerations/ standards (sizing) |
1 |
6 |
0 |
0 |
0 |
0 |
30 |
|
|
Education & training on how all components interact. |
2 |
2 |
4 |
0 |
0 |
0 |
26 |
|
|
Enforcement &
compliance |
3 |
0 |
5 |
1 |
0 |
0 |
23 |
|
|
Changes to the Building Code |
3 |
1 |
4 |
0 |
1 |
0 |
23 |
|
|
Cost/benefit considerations |
5 |
1 |
3 |
1 |
1 |
0 |
22 |
|
|
Research |
5 |
2 |
1 |
2 |
1 |
0 |
22 |
|
|
Interface between
technologies & how they work as a system (technologies includes building
practices & techniques) |
7 |
0 |
3 |
3 |
0 |
0 |
21 |
|
|
Pace of implementation/ incorporating feedback from stakeholders for
implementation |
7 |
3 |
0 |
1 |
1 |
1 |
21 |
Comments and Discussion on Issues
· Philip Fairey: Real issue (1) is getting the knowledge to the user.
· Rob Vieira: Need more research on multi-family housing.
· Roy Crawford: Need research on latent loads; Manual J for dehumidification
· Bob Cochell: Require mechanical plans.
· Steve Bassett: It all boils down to education. Have equipment. If done correctly, will have a good indoor environment. Need to educate consumer, sales reps. Many directional effort re: how to design & install best system. Should be referred to the Education TAC.
· Tina Neace: As system designer, have inadequate information on how to design. Homes are tighter & tighter. No one knows how to do load on some new technologies. Need course on how it interfaces.
· Ivan Zuniga: AFG Glass. Have discussed proper design considerations. Need to consider how building code can be improved to make it simple and enforceable.
· David Martin. Viotech. Set conditions for customer. Seems like need smarter system; not only a thermostat, but also a humidistat. Perhaps outdoor thermostat as well.
· Philip Fairey: If going to make education the priority, would be good if it resulted in certification.
· Dennis Stroer. Need certification of who can do calculations.
· Pete Quintela: Could code mandate design humidity & temperature?
Next Steps
· Bob Cochell. Would like to see CILB involved in education process. Need uniformity in educational process.
· Rick Dixon: Law requires CILB set which courses are required.
The Forum was adjourned at approximately 3:00 PM.
Engineering and Manufacturing Latent Load Removal by Residential Air
Conditioning Systems