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CERV2 Smart, Integrated, Supercharged Dehumidification


Equipment donations from our friends at Mitsubishi (1 ton ducted minisplit heat pump; PEAD-A12AA7 indoor unit, SUZ-KA12NAHZ.TH outdoor unit, and PAC-US444CN-1 thermostat interface) and Aprilaire (E070 dehumidifier) are greatly appreciated!

Ugh! It’s August, and much of North America is muggy. The southeast is hot and humid, while cool maritime moisture humidifies the west coast. And the Midwest seesaws between hot, humid and cool, humid weather.

In this article, we present two examples showing how the CERV2 solves humidity problems. Our first example is a home in the Chicago area that was experiencing higher than desired humidity levels. The second example is CERV2 integrated control of a ducted minisplit heat pump and a ducted dehumidifier on our own building in Urbana Illinois. In both cases, the CERV2’s plug-n-play design makes integration of other components a snap!

The CERV2 does more than control air quality, temperature and humidity in a seamless manner. CERV2 integrated moisture management supercharges dehumidification by increasing both dehumidification capacity and dehumidification efficiency! Read more to learn why.

Moisture Management

The hidden (“latent”) nature of moisture control masks its significance. A recent control screen photo from the CERV2 at our Build Equinox facility shows an indoor temperature of 73F and 53% relative humidity while outdoor conditions are 71F with 99% relative humidity. Note that our high performance, 4500 square foot building is being kept at a comfortable 73F and 53% relative humidity with only a 1 ton Mitsubishi ducted minisplit and an Aprilaire ducted dehumidifier integrated and controlled with a CERV2 smart ventilation unit.

30% more energy must be removed from air at 71F and 99% relative humidity air than must be removed from air at 100F and 20% relative humidity to maintain 71F and 50% relative humidity! Uncontrolled humidity impacts our health and productivity. High humidity increases dust mite activity that triggers asthma attacks, high humidity encourages mold and mildew growth that degrades our health and buildings, and uncontrolled variations of humidity warps and shrinks materials such as wood in flooring, furniture and musical instruments. We lose our ability to cool by perspiration evaporation as indoor humidity increases above 60% relative humidity, but our bodies don’t realize this and continue producing excessive, ineffective sweat.

The need for moisture management increases as our homes are sealed and insulated. Unfortunately, today’s high SEER air conditioners are moving in the opposite direction with reduced moisture management capability. For example, Mitsubishi’s 2010 1 ton, ductless Hyper Heat (MSZ-FE12NA indoor and MUZ-FE12NAH outdoor units) reported a SEER of 23.0 with a moisture removal capacity of 2.9 pints per hour. A few years later, Mitsubishi released a new Hyper Heat unit (MSZ-FH12NA indoor and MUZ-FH12NAH outdoor) with 13% SEER increase to 26.1. Moisture removal capacity dropped 35% to 1.9 pints per hour.

One of the unfortunate consequences of improving SEER values is reduction of dehumidification capability because the factors that enhance SEER numbers (increased fin surface, increased air flow, reduced compressor speed) decrease latent conditioning capacity. Mitsubishi’s ¾ ton units (“09” units) reported 17% SEER gain from 26.0 to 30.5 while suffering a whopping 62% moisture removal loss from 2.1 pints per day to only 0.6 pints per day.

For more information on managing moisture in buildings, read our 4-part “Handling Humidity” report series (Moisture Generation in Homes – Part 1, Climate Moisture Variations – Part 2, Methods for Managing Moisture – Part 3, Putting It All Together House Moisture Modeling – Part 4).

Chicago Area Home Renovation Project

Amy Myers and Mike Baker, aka the “Happy Boolos”, love their neighborhood. Like many others, they wanted to shift their home away from fossil fuel dependence while improving indoor health in their 1964 era home. They hired one of the best architects we know, Mike Kollman, to transform their home into the home of their dreams. Out went the gas furnace, and in came a 5 head Mitsubishi minisplit heat pump for zone-controlled comfort. A CERV2 unit was installed to manage air quality as the home’s insulation and sealing were improved. Read more about Amy and Mikes’ adventure from their website linked above.

Along comes the Illinois summer with its humidity, and the Happy Boolos wanted to improve their ability to keep indoor humidity below 60%. Managing humidity and temperature comfort conditions with only an air conditioner is like fighting with one arm tied behind your back. You might get a few punches in here and there, but you’re going to lose the battle. Effective temperature and moisture management requires an “air conditioner” (air cooler) and a dehumidifier, coupled with a smart controller (CERV2) that understands how to efficiently balance temperature and moisture conditioning needs.

Mike (the homeowner) and Mike (the architect) asked Ben (Build Equinox) how to improve the situation, and Ben recommended integrating Aprilaire’s new Energy Star E080 ducted dehumidifier into the CERV2’s supply to the house. The CERV2 has plug-n-play menu selections for controlling many types of comfort conditioning equipment, including “dehums”.

Here’s where it gets confusing. Mike and Mike agreed with Ben’s advice. They contacted Compass HVAC, owned by another Mike, who sent his lead installer, also named Mike, to Mike’s house to install the E080. Once we sorted through all of the Mikes, the install was easy. Mike (the installer) arrived on Thursday morning (August 12), and finished by noon. Mike (the installer) called us to doublecheck settings on the E080 and CERV2. Mike used the CERV2 menu selections to enable its dehumidifier control function, and set the house humidity setpoint to 55%.

The effectiveness of the CERV2 managing house humidity was immediate. By early afternoon on August 12, The CERV2 had brought the house into moisture control, despite very high levels of outdoor humidity. CERV-ICE (“service”), our free, online monitoring service included with every CERV2, takes the guesswork out of knowing if the CERV2 and its auxiliaries are operating. The Happy Boolos home dropped to 55% humidity and has remained there.

Supercharging Comfort Control with CERV2 Integrated Ducted Minisplit and Ducted Dehumidifier

Integrating a ducted minisplit heat pump and ducted dehumidifier with a CERV2 smart ventilation unit supercharges a home’s dehumidification capacity and dehumidification efficiency. Synergistic performance of CERV2, ducted minisplit and ducted dehumidifier results in exceptional IAQ, temperature and humidity control. A bonus is the CERV2’s clean, filtered (MERV 13) air supplied to both minisplit and dehumidifier units.

No additional mechanical room space is needed for an integrated minisplit and dehumidifier system because the units nest together above the CERV2. The CERV2’s plug-n-play operation simplifies integrated comfort and humidity control!

Indoor and outdoor humidity plots showing CERV2 control of humidity maintains +/-3% humidity variations around the 55% relative humidity setpoint. CERV2 humidity control disabled from Aug 11-12.
Build Equinox’s 4500 square foot building temperature control during August 2021. Note that the CERV2 automatically took advantage of cooler weather conditions, using its “free conditioning” and “energy saver” modes to reduce indoor building temperatures. During hotter weather, the CERV2 automatically engaged the integrated Mitsubishi heat pump to maintain 73F indoor temperature. CERV2 control settings were unchanged during this time period with the exception of disabling humidity control on August 11-12.

August 2021 plots of indoor and outdoor humidity and temperature for our Build Equinox building demonstrate the effectiveness of CERV2 controlled comfort. The first part of August was cool and humid, followed by hot and humid weather, and a second cooler but still humid weather period.

The Aprilaire unit was disconnected and capped from August 11 to 12 to demonstrate operation without humidity control. Our Build Equinox building climbed to 65% relative humidity within a couple of hours. Building humidity continued to increase to 75% relative humidity. We re-connected the dehumidifier on August 12, with the CERV2-Mitsu-Aprilaire system restoring the building back to 55% relative humidity within a day.

Temperature remained in control throughout August, with the CERV2 modulating and alternating between “free conditioning” during nice weather (equivalent to automatically opening windows, except fresh air from the CERV2, unlike an open window, is filtered). As warmer weather returned in mid-August, the CERV2 increased its cooling capacity, and then added the Mitsubishi’s cooling capacity as needed. Note that the CERV2 “inverter drive” (speed control) compressor modulates its capacity to achieve an integrated system performance higher than the individual ducted minisplit operation.

More Than Meets the Eye

The CERV2 modulates its capacity and power as it controls the minisplit heat pump and dehumidifier units. Efficiencies of both minisplit and dehumidifier are increased by the CERV2’s integrated “psychrometric” control operation. CERV2 coordinated operation of IAQ and comfort (temperature and humidity) is more than just simply switching units on and off.

Integrated CERV2-Mitsubishi-Aprilaire dehumidification capacity is increased by more than 300% and dehumidification efficiency is doubled in comparison to conventional, non-integrated operation! The secret to enhanced moisture performance is the CERV2’s ability to condition fresh, filtered outdoor air before it mixes with indoor air. Conventional comfort conditioning systems dehumidify indoor air after outdoor ventilation air has mixed with indoor air.

Throughout the 2021 summer, we have collected performance data from combined CERV2-Mitsubishi-Aprilaire integrated operation. The data is real data. That is, our 4500sqft Build Equinox facility is actively controlled under real world conditions, and we are experiencing the resulting comfort directly.

Outdoor conditions for our summer test (open squares) of integrated CERV2-Mitsu-April indoor air quality management and comfort control. The small data points are hourly weather data for Urbana Illinois for 2010. Average monthly conditions for central Illinois are shown by the thin black line between 60 and 80% relative humidity. The thicker black line outlines the extent of central Illinois weather.

The figure above shows our test data (open squares) on a psychrometric (temperature versus humidity) plot. Also shown on the figure is hourly data from 2010 for Urbana Illinois, monthly average temperature and humidity conditions for Urbana, and a line that outlines Urbana hourly data. Each test data point represents approximately 1 to 2 hours of operation (some data points are shorter and some are longer time periods) in which we monitored the power, temperature, humidity, and condensate of each unit (CERV2, Mitsubishi ducted minisplit, and Aprilaire E070 dehumidifier). Most data points are for outdoor air (fresh air vent mode) passing through the CERV2, and then split between the minisplit and dehumidifier units.

We operated in multiple manners with varying levels of air flow, and CERV2 operation modes. For example, we alternately operated the CERV2 in cooling mode and “off” mode in order to determine the CERV2’s air pre-conditioning benefit to minisplit heat pump and dehumidifier operation. Typical airflows for combined operation were 400 to 450cfm with the ducted minisplit receiving up to 300cfm and the dehumidifier receiving 150cfm. Fans for all three units interacted in a beneficial manner, with no fan resonance or air flow interference over all combinations of unit operation and fan speed modulations (the Aprilaire is a fixed speed fan while the CERV2 and Mitsubishi units can modulate air flow).

A plot of combined system dehumidification capacity data from our tests show moisture removal capacity increases as humidity ratio increases. Humidity ratio is the ratio of water vapor mass to air mass, and a humidity ratio of 0.01 indicates that approximately 1% of a room’s air is water vapor (by mass). Humidity ratios between 0.008 and 0.01 are preferred for indoor comfort, which is 50 to 60% relative humidity at typical indoor temperatures (71-72F or 22C).

At room condition humidity ratios (0.008 to 0.01), combined system dehumidification capacity is 1.5liters per hour (76 pints per day). Data points (yellow) denoted as “room condition” were collected with the CERV2 in recirculation mode, in which room air passed through the CERV2, minisplit heat pump and dehumidifier units. All other data points shown were from “fresh air venting” operation in which outdoor air passed through the CERV2 (with and without CERV2 pre-conditioning outdoor air) before passing through the minisplit heat pump and dehumidifier.

Combined CERV2-Mitsu-Aprilaire dehumidification capacity. During fresh air venting, the CERV2 efficiently pre-conditions air for dehumidification by the Mitsubishi and Aprilaire units. The more humid the outdoor air becomes, the greater the dehumidification capacity. The room condition data shows the dehumidification capacity if outdoor air is allowed to mix with indoor air before dehumidification.

Dehumidification performance increased as humidity ratio increased. At the highest humidity ratio (0.023), total system dehumidification increased to 6 liters per hour (304 pints per day)! Rainy day performance is marked on the plot with very high dehumidification capacity occurring at relatively low humidity levels. The rain lasted for 2 to 4 hours. During the rain, humidity levels were below water vapor saturation (100% relative humidity), however, dehumidification rates were very high. We speculate that aerosolized rain droplets were entrained in fresh air to the CERV2. Although such droplets would be caught in the CERV2’s MERV 13 filter, water passes through the filter unlike dirt that is captured in the filter material. As the rain ended, humidity levels increased, with the system’s performance moved toward other data points collected during non-precipitation periods.

Combined CERV2-Mitsu-Aprilaire dehumidification efficiency expressed in Liters per kWh of condensate collected also increases significantly as humidity increases.

Dehumidification efficiency also increases as humidity increases. At room condition humidity levels, dehumidification efficiency was found to be 1liter per kWh. The Energy Factor, EF, for the combined system more than doubled to 2.5 liters per kWh as humidity increased. Rainy day data points show very high levels of performance, possibly due to aerosolized droplets impinging on the wet cooling coils, adding to condensate recovered without needing to be condensed. Note that these droplets would have passed into the indoor environment in conventional systems where they would vaporize and need to be removed by dehumidification.

The combined dehumidification efficiency is low compared to “Energy Star” dehumidifier efficiency listings because Energy Star listings neglect the energy required to remove heat from dehumidifiers. Aprilaire dehumidifiers are top performing units with Energy Star performance levels of 2.35 liters per kWh. Part 3- Methods for Managing Moisture from our Handling Humidity report series explains why actual dehumidifier performance is different than Energy Star test ratings (see Figure 19, page 24). A dehumidifier with an EF of 2.35liters per kWh based on 80F and 60% relative humidity test conditions has an actual performance of 1liter per kWh at a temperature of 70F when the impact of its internal heat load on building conditioning is included in the efficiency rating.

In summary, our performance tests indicate the following:

1) Removing moisture from humid air before it mixes with indoor air can more than triple dehumidification capacity

2) Removing moisture from humid air before it mixes with indoor air can more than double dehumidification efficiency

What about alternative methods for managing humidity? Don’t ERVs automatically manage moisture in humid regions? The short answer is, no, ERVs do not effectively manage humidity even though they are commonly thought to do so. When an ERV is ventilating a 100% humidity bathroom, moisture is added to incoming fresh air, even in humid Miami and Houston. For the longer answer (but with real field data) demonstrating poor humidity control with ERVs, read Build Science Corporation’s report on moisture management in homes.

CERV2 Integrated Control of Moisture…Will it play in Peoria, or Miami?

A CERV2 integrated minisplit heat pump and dehumidifier works great in Urbana Illinois, and because we have the same weather, it will do well in Peoria, but what about elsewhere? A psychrometric plot for Miami showing hourly weather data from 2010 and Urbana’s weather “envelope” and test data conditions verify that we can handle as high of humidity conditions that Miami can dish out. Place our 1988 vintage, 4500sqft Morton Building in Miami, or Houston, or anywhere in North America, and our CERV2 with 1 ton ducted minisplit and ducted dehumidifier system will keep both temperature and humidity in control more efficiently than any other system!

Miami is one of the most humid regions in North America, but our central Illinois weather conditions cover the worse humidity Miami experiences. Miami also has monthly relative humidity between 60 and 80% as in Illinois. The red line shows Miami’s monthly average conditions while the thicker black line that envelopes central Illinois weather is larger than Miami’s hourly weather extremes.

Read Part 4- Putting It Altogether; House Moisture Modeling of our Handling Humidity series to see why smart ventilation is much more efficient than constant flow ventilation systems, and why smart ventilation is essential for keeping air healthy. Conventional constant flow ventilation systems are only good at keeping air healthy when you are not at home.

The psychrometric plot above schematically depicts hot-humid, cool-humid, hot-dry, and cool-dry regions. Much of North America experiences significant periods of both hot-humid and cool-humid conditions. We will demonstrate how to determine how to determine moisture removal and energy for dehumidification for Urbana and Miami.
Two tables from Part 2- Climate Moisture Analysis of our Handling Humidity report series show the fraction of a year Urbana and Miami spend in each of the four psychrometric quadrants. Miami is in hot-humid conditions for 75% of the year while Urbana spends 23% of the year in hot-humid conditions.
Pie charts for several locations showing outdoor time fractions for psychrometric quadrants.

Pie charts showing comfort quadrant time fractions for several US locations are also attached. The pie charts (from Part 2 of Handling Humidity reports) are organized in a roughly geographic placement, showing how comfort conditioning varies as one moves north to south and east to west. The west coast primarily requires dehumidification due to cool-humid conditions while the east and Gulf coast are dominated by warm-humid conditions. Throughout much of the Midwest, significant periods of warm-humid and cool-humid conditions require moisture management. The intermountain and Great Basin regions, as observed for Denver, have low dehumidification requirements.

Fresh air brought into a house is more efficiently dehumidified when it is directly conditioned by the CERV2 integrated system as described in the previous section. Over the course of a year, one person should have a minimum of 20cfm (cubic feet per minute) of fresh airflow per person. This is somewhat greater than standard building ventilation conditions (ASHRAE 62.2-2019), but is half of the 40cfm per person that Build Equinox recommends for a truly healthy indoor environment. We will assume 20cfm per person for our examples, but stress again, the building industry needs to increase their fresh air standards!

A fresh air ventilation rate of 20cfm per person is equivalent to 1000kg of air (a metric ton) per person blown into (and out of) a house per day! We can determine how much water must be condensed from this air for Urbana and Miami (and several more locations with tabular data in Part 2 of Handling Humidity). The following relation calculates the total amount of water that must be removed from ventilation air during humid conditions:

Mwater = Mair x F x 365days x (Wo – Wi)


Mwater = water removed from ventilation air per year (kg or liters)

Mair = ventilation air mass blown through a house per day

F = fraction of year with humid conditions (for cool-humid and warm-humid periods)

Wi = indoor humidity ratio (=0.0089 for 72F and 55% relative humidity indoor air)

Wo = average outdoor air humidity ratio for cool-humid or warm-humid quadrants

Urbana Example:

Urbana is in warm-humid conditions for 22.7% of the year with an average outdoor humidity ratio (Wo) of 0.016 (remember, humidity ratio is simply the ratio of water vapor mass per dry air mass). The amount of water per person per year that must be removed during Urbana’s warm-humid season is:

Mwater = 1000kg-air/day-person x 0.227 x 365days/year x (0.016 – 0.0089)kg-water/kg-air

Mwater = 574kg-water per person per year removed from ventilation air during warm-humid conditions

A similar calculation shows that 111kg-water per person must be removed from ventilation air during Urbana’s cool-humid season.

Once we know the amount of water removed and the average weather conditions, we can determine the electrical energy needed to remove the moisture. As described previously, conventional fresh air ventilation systems mix outdoor air with indoor air, which reduces dehumidification capacity and efficiency. From our dehumidification system efficiency plot (Liters per kWh versus humidity ratio), we see that the components we’ve integrated into the CERV2 operate at 1liter per kWh at room condition humidity ratios (~0.008 to 0.01). During Urbana’s warm-humid period, dehumidifying outdoor air at an average outdoor humidity ratio of 0.016 increases the dehumidification efficiency factor to 2liters/kWh (and dehumidification capacity to 4 liters per hour). Dehumidification energy is calculated as:

Outdoor air mixed with indoor air:

Edehum = Mwater / EF = 574kg-water / 1liter per kWh = 574kWh per person per year

Outdoor air conditioned directly by CERV2 integrated system before mixing with indoor air

Edehum = Mwater / EF = 574kg-water / 2liters per kWh = 287kWh per person per year

Assuming an electricity cost of 12 cents per kWh, conventional dehumidification cost $69 per person per year for ventilation air moisture removal versus $35 per person per year for ventilation moisture removal for the CERV2 integrated conditioning system. A home with 2 to 4 occupants would save $68 to $136 per year with the CERV2 integrated system. The 287kWh per person energy difference between conventional dehumidification and CERV2 integrated dehumidification would power an EV (Electric Vehicle) 1000 miles per year!

Miami Example:

A similar calculation for Miami shows 1880 liters of water removal from ventilation air per person per year for Miami’s warm-humid season! Conventional dehumidification with ventilation air mixed with indoor air before conditioning requires 1880kWh per person per year for electric energy compared to integrated CERV2 direct conditioning of ventilation air requiring 940kWh per person per year. Assuming 12 cents per kWh, Miami’s warm-humid period costs $226 per person per year compared to $113 per person per year for integrated CERV2 direct processing of ventilation air. Note that Miami’s average warm-humid season conditions are quite similar to Urbana conditions, however, Miami spends 75% of the year at this condition compared to 23% for Urbana.


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