Why Temperature Is Only Half the Story
Three-part Summer Series 2026 | automatedbuildings.com
Summer looks different depending on where your building sits. Florida’s Gulf and Atlantic climates combine high dew points with heavy outdoor air moisture loads, making moisture removal as hard a problem as temperature control. Texas combines subtropical humidity in the east with a grid structure where peak summer afternoons can turn latent load into a demand cost issue. Las Vegas designs cooling systems for triple-digit outdoor air temperatures, and Nevada’s grid faces enough data center pressure that NV Energy’s CEO has said load in the region could quadruple in the coming years. California spans 16 climate zones as defined by the California Energy Commission, from coastal fog in San Francisco to desert heat in the Coachella Valley, with wildfire smoke adding an air quality dimension that barely existed in building automation specifications a decade ago.
These markets share one failure mode. A cooling system that manages temperature but ignores moisture is only doing half its job.
Key numbers
- 16 California climate zones, per the California Energy Commission
- At least 25 percent of commercial rooftop units in the field are oversized, per ENERGY STAR
- 15 to 42 percent site energy savings from VRF versus rooftop VAV systems, per Oak Ridge National Laboratory
- 4x potential grid load growth in parts of Nevada from data center demand
Sensible vs. Latent: The Psychrometric Basics
A cooling system has two jobs. Lowering air temperature gets measured, setpoint, and noticed when it fails. Removing moisture stays invisible until it goes wrong. In hot, humid climates, latent load can represent a major share of total cooling load, large enough to drive overall system performance, not just comfort. Automation that does not explicitly manage that load is doing half the job.
Sensible heat changes a thermometer reading. Latent heat changes moisture content without changing temperature. Removing both requires driving air below its dew point long enough for moisture to condense and drain away, which needs sustained equipment runtime and cannot be rushed by oversizing the unit. Oversizing actively works against it.
An oversized system reaches setpoint quickly and shuts off. The short cycle means supply air never stays cold long enough to pull real moisture out of the space. Relative humidity climbs even as the thermostat reads comfortable. Short cycling can materially increase energy use once parasitic losses, fan operation, poor staging, and moisture re-evaporation off the coil are counted, on top of accelerated compressor wear. ENERGY STAR puts the scale of the problem in context: at least 25 percent of commercial rooftop units in the field are oversized.
The BAS rarely catches this because the temperature setpoint is being met. If relative humidity is not trended and alarmed, the failure stays invisible until occupants complain or an inspection finds moisture damage.
Why Dew Point, Not Relative Humidity, Should Drive the Strategy
Relative humidity is the number most BAS trends, and the one most likely to mislead. It is a ratio that moves whenever temperature moves, even if the air’s actual moisture content has not changed. Dew point measures moisture directly and does not shift just because a fan sped up or a damper opened.
Temperature alone is not enough. A BAS that trends only zone and discharge air temperature can miss the real failure. Dew point, relative humidity, outdoor air conditions, coil runtime, damper position, and ventilation mode all belong in the latent load story. The question is not just whether the mechanical system can remove moisture. It is whether the controls strategy knows when moisture is entering, whether the coil runs long enough to remove it, and whether the building is drifting toward a humidity problem while the thermostat still looks satisfied.
Dedicated Outdoor Air Systems and the Latent Load Strategy
One effective response is to treat latent load separately. A dedicated outdoor air system, or DOAS, handles ventilation air independently of the sensible cooling system. Incoming outdoor air, carrying both heat and moisture, is pre-conditioned before it enters the occupied space, leaving the primary cooling system to handle more of the sensible load from occupants, lighting, equipment, and the envelope.
Desiccant wheels are increasingly common in DOAS installations for humid climates. A desiccant wheel uses hygroscopic material to pull moisture from incoming air and transfer it to an exhaust stream, running continuously without the very low temperatures refrigerant based dehumidification requires. Other approaches, including a DOAS paired with a standard coil, heat pipe assist, energy recovery ventilation, reheat, or chilled water reset, can also manage latent load depending on the building. In markets like Houston, Miami, and coastal Florida, where peak summer outdoor air can carry an enthalpy load rivaling the mechanical load itself, treating latent control as optional is a specification error.
DOAS is not just equipment, it is a control sequence. A well selected desiccant wheel or energy recovery unit can still underperform if supply air dew point, reheat staging, airflow, or occupancy scheduling are sequenced wrong. The mechanical design gets the credit, but the controls layer usually decides whether the strategy works in the field.
Variable Refrigerant Flow and Humidity Management
VRF systems modulate compressor speed continuously to match real time demand, a real advantage over staged rooftop equipment in humid climates. Because VRF can run at low capacity for extended periods instead of cycling on and off, it holds the supply air conditions needed for sustained moisture removal even when sensible demand is modest. Oak Ridge National Laboratory research puts VRF site energy savings at 15 to 42 percent versus rooftop VAV systems, with source energy savings of 18 to 33 percent. Other published studies report higher savings under specific conditions, so results vary with climate, load profile, and commissioning quality.
For buildings with variable occupancy, VRF also enables zone level control, so humidity management follows actual conditions rather than a fixed schedule. An empty Tuesday morning conference room does not need the same latent load treatment as the same room at full capacity in the afternoon.
KMC Controls, manufacturer of BACnet native building automation solutions, addresses this directly. The KMC FlexStat integrates temperature and humidity sensing in one device, paired with adaptive occupancy programming that adjusts heating, cooling, and ventilation based on learned behavior in the space. In small and medium commercial buildings where dedicated humidity infrastructure is impractical, that embedded sensing and control logic closes a gap that would otherwise go unaddressed.
The Demand Controlled Ventilation Intersection
Demand controlled ventilation uses CO2 sensors to adjust outdoor air intake based on actual occupancy rather than design maximum assumptions, directly relevant to latent load in humid climates. Every cubic foot of outdoor air entering a Florida or Texas building in summer arrives pre-loaded with moisture. Over-ventilating an empty space imports humidity it does not need. Department of Energy research shows CO2 based DCV has its greatest savings potential where occupancy fluctuates and peaks high, with commercial energy savings commonly in the 10 to 30 percent range and higher in some studies. Savings vary by occupancy pattern, climate, and commissioning.
DCV saves energy by reducing outdoor air, but it must never undercut ASHRAE 62.1 minimum ventilation rates or indoor air quality targets. It is a way to avoid over-ventilating, not a license to under-ventilate.
Economizers deserve the same caution in humid climates. A standard dry bulb economizer can bring in outdoor air based on temperature alone, and in a hot humid market that air can be cool enough to satisfy the logic while still carrying a heavy moisture load. Without an enthalpy or dew point lockout, an economizer that looks efficient can quietly import the exact latent load problem this article addresses.
What the BAS Actually Needs to Trend
A latent load is a control problem hiding inside a mechanical problem. Equipment, whether DOAS, VRF, or a conventional rooftop unit, performs only as well as the sequence managing it. At minimum, the controls layer should trend and alarm on:
- Dew point, alongside relative humidity
- Cooling coil or compressor runtime
- Discharge air dew point or leaving air temperature
- Outdoor air damper position and economizer lockout status
- Space relative humidity and dew point
- Ventilation mode and CO₂ levels where DCV is in use
A building trending only zone temperature looks fine on paper until an occupant reports a musty smell or an inspection finds damage behind a wall. The mechanical system determines what is possible. The controls sequence determines what actually happens.
Sources
- California Energy Commission: Climate Zone Tool, Maps, and Information — https://www.energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/climate-zone-tool-maps-and
- Title 24 Express: Title 24 California Climate Zones Overview — https://www.title24express.com/what-is-title-24/title-24-california-climate-zones/
- ENERGY STAR: Right Sized Air Conditioners Fact Sheet — https://www.energystar.gov/ia/home_improvement/home_sealing/RightSized_AirCondFS_2005.pdf
- Oak Ridge National Laboratory: Evaluation of Energy Savings Potential of VRF from VAV in U.S. Climate Locations — https://impact.ornl.gov/en/publications/evaluation-of-energy-savings-potential-of-variable-refrigerant-fl/
- U.S. Department of Energy: Ultra-Low SWaP CO2 Sensing for Demand Control Ventilation — https://www.energy.gov/cmei/buildings/articles/ultra-low-swap-co2-sensing-demand-control-ventilation
- Las Vegas Review-Journal: Data Centers and Nevada Grid Capacity — https://www.reviewjournal.com/news/environment/unprecedented-data-centers-want-to-triple-nevadas-energy-grid-capacity-3462716/
- Novva: NV Energy CEO on Nevada Grid Load Projections — https://www.novva.com/media-center/why-nevada-is-the-silver-states-golden-opportunity-for-data-centers/
Further Reading from Our Archive
Measuring the Right Thing for Humidity Control: It’s the Dew Point Stupid
https://www.automatedbuildings.com/news/aug04/articles/airtest/airtest.htm
Why relative humidity is the wrong control variable and dew point or grains per pound should drive dehumidification strategy.
Challenges in QSR Due to High Energy Intensity
https://www.automatedbuildings.com/2026/06/challenges-in-qsr-due-to-high-energy-intensity/
DOAS and enthalpy load challenges in Houston, Miami, Phoenix, and Charlotte, a strong parallel case study for hot humid climate design.
Chilled Beam Application and Control
https://www.automatedbuildings.com/news/feb12/articles/alc/120124021101alc.html
Dew point based condensation control in decoupled sensible and latent systems, relevant background for DOAS sequencing.
ASHRAE Standard 62 Dehumidification Requirements: Update, Analysis and Recommendations
https://www.automatedbuildings.com/news/jan06/articles/ebtron/ebtron.htm
Background on the 65 percent relative humidity design threshold and ASHRAE 62.1 dehumidification requirements referenced throughout this series.
ASHRAE Standard 62 Ventilation for Acceptable Indoor Air Quality: Requirements for Compliance
http://www.automatedbuildings.com/news/aug02/articles/ebtrn/ebtrn.htm
Original coverage of the Addendum x dehumidification and building pressurization requirements referenced in this series.
Part 2 of this series looks at how building automation and AI-driven platforms are changing the economics of hot weather operations, including predictive pre-cooling, thermal energy storage, and fault detection strategies that catch equipment degradation accelerated by heat before it becomes a failure. Part 3 closes out the series with policy, code, and the autonomous building future, looking at how evolving energy codes and AI driven control are reshaping what hot climate buildings are expected to do on their own.
