This Article Is About A Whole-House Energy Recovery Ventilator + Two Additional Types Of Energy Recovery Ventilators

• Energy Recovery Ventilator (ERV).  ERV is for areas that have summers with moderate humidity levels.

• Dehumidifying Energy Recovery Ventilator (DERV).  DERV is for areas with summers having high humidity levels.  This is the best choice for DFW. 

• Heat Recovery Ventilator-HRV.   HRV is only for cold winter climates. 

Al’s Plumbing, Heating & A/C, in Plano, Texas provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s Plumbing, Heating & A/C is near your home in Plano, Allen, and Frisco.  We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge. We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge.

Energy Recovery Ventilator (ERV), Dehumidifying ERV (DERV) 

& Heat Recovery Ventilator (HRV)  

Which One Do You Need In DFW?

Shown: This Is What An ERV, DERV, & HRV Looks Like With Its Front Cover Removed

Image Source: Amazon

Why A Whole-House Energy Recovery Ventilator Is Needed In Newer Homes

Image Source: Pixabay

Today’s Newly And Recently Built Homes Are Quite Airtight.  They Cannot Have More Than 5 Air Changes Per Hour (ACH). 

An Air Change Per Hours Is A Complete Exchange Of Indoor Air With Outdoor Air During 1 Hour.  This Occurs Due To Air Leakage Into The Home.

Image Source: ShutterStock

As Compared, A Home Built During The 1970’s Has Up To 17 ACH!   

If a new home is leaking as little as 3 ACH, it is leaking only 18% of the air as that a 1970’s built home leaks.  By building homes more airtight, their energy use for cooling & heating is dramatically reduced.   This, does however, create a new problem.  The build up of pollutants & humidity inside the home.  To solve these problems, controlled mechanical ventilation is required to ensure at least 3 ACH.  This is the minimum number of ACH required to ensure acceptable Indoor Air Quality.   The best type of Energy Recovery Ventilator depends on the location of the home within the U.S.

Today’s New Homes Are Rated For Energy Efficiency Using The Home Energy Rating System (HERS)    

With over 2.4 million homes rated in the US, the HERS Index is the industry-standard for rating a home’s energy efficiency.   HERS is also the nationally recognized system for inspecting and calculating a home’s energy performance.

The lower the HERS Score, the more energy-efficient the home is.  The HERS Score in partly determined by the results from 1. Air-Infiltration testing + 2. Ductwork Leakage testing.   The lower the HERS Score is, the more airtight the home is.  The numbers below help to understand why new and newer homes require Mechanical Ventilation.

• HERS score = 150.  A home built in the 1970’s.
• This home uses +50% more energy for cooling & heating than a HERS = 100 home (see below).

• HERS Score = 100 is a standard-efficiency home built in compliance with the 2004 International Energy Conservation Code (IECC) Building Codes.

• HERS Score = 85.  An Energy Star Certified Home.  This home uses -15% less energy than a HERS = 100 Score home.

• HERS Score = <54   The 2019 HERS Score Winner was Lennar Homes Of Minnesota.  During 2018, 81% of their homes built had a HERS Index Score under 54.
• These homes use nearly 1/2 less energy than a HERS = 100 (Standard-Efficiency) Home.

• HERS Score = 0.  A “Net Zero: Home.
• A true Net-Zero home is all electric.  The home creates as much electricity (with solar collectors) as it uses each year.  A Net-Zero Home creates no energy bills over the course of any individual year.

Click Here To Learn About: Net-Zero Energy Homes

Click Here To See: HERS Score Tag For Existing, Energy Star Certified & Reference Home

ERV, Dehumidifying Ventilator (DERV) & HRV  

This article describes the 3 types of mechanical ventilators that recapture the heat or cool from the air being exhausted.   There are other mechanical ventilation methods used by some new home builders that consist of a very quiet exhaust fan running 24 hours a day.  This fan is typically in the owner’s suite bathroom (the most likely source of humidity).

This type of mechanical ventilation resolves the indoor air pollution problem.  However, it removes heated & cooled air and replaces it with hot or cold outdoor air through air leaks in the house.    If your owner’s suite bathroom has 2 exhaust fans, and one cannot be shut complete off  OR there is an adjustable-speed fan, that cannot be shut completely off, your home likely has this type of mechanical ventilation.

NOTE:  Don’t disable this type of exhaust fan.  It’s there to ensure acceptable Indoor Air Quality.  If you shut it off, pollutants & humidity will build up inside your home.

NOTE:  Some large bathrooms may have two exhaust fans.  Typically 1 is near the shower and 1 is near the toilet.   If both fans can be completely shut off, neither fan is for mechanical ventilation.

The Most Common Indoor Pollutants

Homes have several sources that contribute to indoor air pollution.   Some of the most common sources are:

      POLLUTANT:                    SOME SOURCES:

1. Radon                                  Comes from the soil under the home, and possibly other sources.
2. Tobacco Smoke                 Secondhand Smoke
3. Biological Sources            Mold is one example.
4. Carbon Monoxide            From gas cooking appliances and possibly air leaks between the garage and living space.
5. Nitrogen Dioxide             Nitrogen dioxide (NO2) comes from the same sources as carbon monoxide.
6. Volatile Organic Gases   What you smell when you use cleaning products, nail polish, nail polish remover and other grooming products.
7. Breathable Particles        Dust, mold spores.
8. Formaldehyde                  Glues, environmental tobacco smoke, textiles and other sources.
9. Pesticides                          Pesticides.
10. Asbestos                            Homes built 1930 — 1970 are likely to have asbestos-related products.   Common products were; insulation, roofing materials, asbestos cement and others. **

If too little outdoor air enters a home, pollutants may accumulate to levels that pose health & comfort problems.  New homes do not leak enough air to ensure acceptable Indoor Air Quality (IAQ) so they must have mechanical ventilation equipment.

** Source: https://www.mesotheliomadiagnosis.com/asbestos/products/

Three Primary (Energy Recovery) Ventilation Systems Are Used In Newly Built Homes Today:  

ERV, DERV & HRV All Perform Identical Ventilating Functions.

The Difference Between The 3 Is Their Ability To Help Control Humidity (ERV), OR To Remove Humidity (DERV) Of Incoming Air.

Image Source: ShutterStock

SHOWN: Air-Flow Through ERV, DERV, & HRV

IMAGE COLORS KEY:

OUTSIDE: 

• RED: Fresh (Hot) Air Entering The Ventilator During Summer.
• PURPLE:  Stale House Air Exhausted From The Ventilator.

INSIDE:

• LIGHT BLUE:  Stale Indoor Air Entering the Ventilator
• DARK BLUE: Refreshed Air Leaving Ventilator and Into The Home.
• Refreshed Air is a mixture of recycled indoor air + some new outdoor air mixed in.  The ventilator exhausts the same amount of stale air from the home as it brings in as fresh air.

DARK GRAY DIAMOND:  This is the Energy-Transfer Core.

• Indoor stale air enters the ventilator and is refreshed by adding some fresh outdoor air.
• During summer, the Energy-Transfer Core Extracts Cool From Outgoing Air.   During winter, it extracts heat From Outgoing Air.
• During Summer, Incoming Air is pre-cooled (with the cool extracted from outgoing air)  while in the Energy-Transfer Core.
• During Winter, Incoming Air is pre-heated (with the heat extracted from outgoing air) while in the Energy-Transfer Core.

Energy Recovery Ventilator (ERV)

An ERV can help control (but not reduce) indoor humidity by transferring some of the humidity from the dryer air-stream into the more humid air-stream.  This helps to reduce the amount of humidity that enters the home through the ERV during summer.  It also limits the amount of humidity that leaves the home during winter.

When outdoor air is more humid than indoor air, an ERV cannot remove enough humidity from the incoming air to reduce humidity inside the home.  On really humid days (which are the norm in DFW) an ERV will likely raise indoor humidity level because it can not exchange ALL the humidity between the two air streams.   The air conditioning dehumidifies, and on really humid days, the A/C may have to be set to a lower temperature in order to dehumidify the air enough.

Variable-Speed HVAC Systems have the ability to slow the furnace blower-fan speed to reduce indoor humidity level.  When air is moved over the cooling coil (inside the furnace or ductwork and cannot be seen without removing a panel) more slowly, more humidity is removed from that air.

• An ERV is suited for warm to hot summer climates with moderate outdoor humidity during the cooling season.    

Dehumidifying ERV (DERV) 

For very humid summer climates such as DFW, a Ventilating Dehumidifier is what’s best.  A Ventilating Dehumidifier performs the same ventilating functions as an ERV.  It mixes  some fresh outdoor air into your home’s recycled air.  At the same time, it removes some stale indoor air, to ensure constant ventilation and Indoor Air Quality.  A DERV also dehumidifies incoming air.

• An DERV is suited for hot summer climates with high outdoor humidity during the cooling season.   This is DFW’s summer climate.

NOTE:  A DERV does not dehumidify recycled air, only the fresh air entering the home.  Whole-House Mechanical ventilators are designed to mix some fresh outdoor air within the recycled air passing through the furnace.   A DERV removes excess humidity from the outdoor before it enters the house.  Recycled air does not pass through the Whole-House Ventilator.   To Remove Humidity From The Recycled Air. A Whole-House Dehumidifier Can Be Added To The HVAC System.

During Summer In DFW:

The A/C does most of the dehumidifying.

During Winter In DFW:

• When the air is coming from the south (gulf of Mexico & Mexico itself) — that air’s humidity level will be higher.

• When the air is coming from the north (the northern U.S. & Canada) — that air’s humidity level is quite low.

Heat-Recovery Ventilator (HRV)

An HRV is only for cold winter climates with mild summers.   An HRV stores heat from exhausted air during winter, and uses it to pre-heat incoming air.  In the summer, it stores the cool from the exhausted air, and uses it to pre-cool incoming air.  Like an ERV, a Heat Recovering Ventilator (HRV) brings ALL the humidity within incoming air into the house. .

DFW’s Weather During Summer and Winter

Dew Point & Air Masses Definitions

To Better Understand Why A DERV Is A Better Choice Than An ERV In DFW, We Provide Some Details About DFW’s Summer and Winter Weather. 

Humidity level is typically stated as “Dew Point”.   Technically, the Dew Point is the temperature at which the water vapor within the air becomes cool enough for it to condense into liquid water drops.  In non-technical terms, Dew Point is the temperature at which dew forms on grass & cars overnight.  The higher the dew point temperature, the more humidity exists within the air.

Weather forecasters track large areas of warm or cold air called “air masses.”  By definition, an air mass is a large area of air with horizontal width of several hundred miles, up to a few thousand miles with temperatures and moisture that are fairly uniform.

Air masses acquire their uniform surface temperature & moisture characteristics by remaining over one region for an extended period of time.  An air mass sitting over a warm, tropical ocean will become warm and humid.  An air mass sitting over the North Pole will be very cold and dry.  Air masses are designated as “Maritime” — originating over the ocean, OR “Continental” — originating over land.

DFW’s Weather Is Categorized as Humid Sub-Tropical During Summer And InterContinental During Winter. 

DFW’s Summer Weather

During summer, DFW’s weather is affected by Maritime-Tropical (mT) air masses originating over the Gulf Of Mexico and Caribbean Sea.  Additionally, there are Continental air masses originating in Mexico.  These air masses move northward into north Texas and beyond.   These air masses are hot and very humid.

DFW’s Winter Weather

• Continental-Polar (cP): DFW’s winter weather is affected by cold air masses, with low humidity & dew points, that form over Canada and / or the northern United States.

• Continental-Arctic (cA): Winter’s most frigid air masses. cA air masses are the coldest & driest of all.  These cold & dry cA air masses originate over Siberia and northern Canada.  Their temperatures will be well below zero degrees and with dew point in single digits where they originate.    These air masses are often referred to as “Polar Vortex”.    DFW is affected by these air masses typically only a few times each winter.

• A polar vortex brings exceptionally cold temps to DFW.  The polar vortex is a large area of low pressure with cold & dry air near the Earth’s poles.  The votex weakens during summer and strengthens during winter.  During winter, the polar vortex can expand, shift or even break into pieces.  DFW weather forecasts typically show an air mass that has temporarily moved southward from the north pole.

In January of 2019 DFW was affected by a polar vortex weather event.  When the polar vortex fractured and moved southward, it caused cold temperatures in much of the United States, including north Texas.  Forecasts were for temperatures 25 degrees or colder below normal.   There was more than one polar vortex weather event during DFW winter 2018 / 2019.

The Reason DFW’s Winter Temp’s Bounce Up & Down

The quickly varied winter temperatures in DFW are affected by; Texas’ geographic location, the polar vortex, and El Niño or El Niña.   

• DFW is far enough north to be affected by strong cold fronts coming from the north. 

• Once a cold front moves east, temperatures typically rebound quickly.   

• The extent to which winter temperatures rebound is based upon if ocean surface temperatures are near normal, or if it’s an an El Niño or El Niña winter.   

El Niño is when ocean-surface temperatures are above normal.  This typically results in Texas having an uptick in precipitation and warmer winter temperatures.

La Niña is when ocean-surface temperatures are below normal. This typically results in Texas having lower precipitation and cooler winter temperatures.

How An ERV Can Benefit A Home In DFW

Ideal Indoor Humidity Level is around 50% relative humidity.  Simple devices are available that allow you to monitor indoor humidity level.

Click On Image To; View Product, See Details, or Purchase From Amazon.com

SHOWN: Combination Device Shows Both Indoor Temperature & Indoor Humidity Level.  The Device Also Tracks Recent High & Low Readings. 

• Winter air masses from the north have quite low humidity.  When indoor humidity is low, indoor temperature will feel cooler.
• This often causes the need to warm the house to a higher temperature.

• Winter air masses from the south have above average humidity.  This works well if heat is running, but if temps are high enough to need air conditioning, high humidity can cause the home to feel too warm.
• This often results in the need to cool the house to a lower temperature.

• When a cold air mass comes from the north, outdoor humidity & temperatures drop.

• When an air mass from the north moves east, and an air mass from the south takes over, outdoor humidity and temperatures rise.

• These recurring changes in humidity can lead to the house never feeling comfortable.

• This creates the need to sometimes alternate between heating and air conditioning.

• A DERV removes most of the humidity from the incoming air stream, and helps control indoor humidity.

• An Energy Recovery Ventilator (ERV) transfers some of the humidity from the dryer air-stream into the more humid air-stream.

• This may help with indoor humidity (depending on the humidity in outside air), but not to the extent that a DERV helps. 

This Article Was About A Whole-House Energy Recovery Ventilator Systems + Two Additional Systems

Al’s Plumbing, Heating & A/C, in Plano, Texas provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s Plumbing, Heating & A/C is near your home in Richardson, Garland, and northeast Dallas, TX.  We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge.