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Ductology (Part 1)
Featured Article
Jan 22, 2018

Cost Optimization of Ventilation Ducts

How much should a ventilation system’s ductwork cost? And, how can one determine if an installed duct network performs at an acceptable level? We begin a new topic, “Ductology” with a two-part series that explores these questions.

This Swedish building boldly celebrates its ventilation system.

Ductwork in residences should receive at least as much design attention as walls, roofs and kitchen cabinets. The energy cost associated with ventilation fan operation can easily exceed the energy cost of heat passing through a house’s walls. Unfortunately, duct design is often left as an afterthought. Duct design is complicated and takes time. But, improperly designed ventilation systems last the lifetime of a home, causing a lifetime of excessive cost and worse, poor health.

In part 1, we will focus on ventilation system cost and performance. Part 2 will discuss assessing the performance of installed duct systems. For those interested in duct design methods, such as Manual D or ASHRAE procedures, we recommend The Energy Vanguard’s 4-part series on duct design as a good place to begin.

Engineers were cost optimizing ventilation systems more than 100 years ago. Willis Carrier (yes, that Carrier) was editor of the 1st edition of Fan Engineering published in 1914. A.S.H.&V.E. is today’s ASHRAE. Energy cost in 1914 was $20 per horsepower-year, or about 7.5 cents per kWh in today’s money. And, as stated in this book and is true today, keep duct velocities less than 700 feet per minute in residences to minimize noise and drafts!

Duct Economics

Optimizing the size of ventilation ductwork is analogous to optimizing wall insulation thickness. A “Life Cycle Cost” (LCC) relation is formulated that totals energy cost and installation cost. The combination of energy cost and installation cost that minimizes the LCC is the most economical system.

Engineers have been economically optimizing ventilation systems for more than 100 years, as seen in this page from a 1914 edition of Fan Engineering. Interestingly, after accounting for a 25-fold increase in the dollar (one 1914 dollar ~ twenty five 2017 dollars), the economics and resulting duct sizes are not too different. And the cardinal rule of residential duct flow...keep duct air velocities below 700fpm...was the same in 1914 as it is today.


Figure 1 shows the Life Cycle Cost (LCC) of 100ft long duct systems with 150cfm, 200cfm and 300cfm of airflow. Details of the LCC relation are in the Appendix, but basically, the LCC is the addition of fan power cost over the lifetime of the ventilation system (100 years assumed) and the installation cost (details of duct installation cost are included in the Appendix).

The minimum LCC value for each airflow has been marked on Figure 1. At 150cfm, a 9 inch diameter duct would be most economical. At 200cfm and 300cfm, the most economical duct systems would have 10 inch and 12 inch diameter ducts, respectively. An interesting characteristic of the optimal duct diameter is that it is not dependent on duct length. Although duct installation cost and duct operation (energy) cost are both directly affected by duct length, optimal duct diameter is independent of the duct length!

The two LCC relation factors, duct installation cost and lifetime energy cost, work in opposition to each other. On the left side of the optimum duct diameter in Figure 1, the increase in LCC is due to rapidly increasing energy cost because the required fan power rapidly escalates with decreased duct diameter. On the right side of the optimum duct diameter, increasing LCC is due to the modest escalation of installation cost of larger diameter duct.

If the ventilation system installer decided to scrimp on duct size, or insufficient duct clearance forced a smaller duct than optimal to be installed, the economic and energy cost penalties climb more rapidly. A 6 inch duct would increase LCC by more than $2000 with a 50cfm increase from 150cfm to 200cfm, while a desired increase from 150cfm to 300cfm would increase LCC by $7000!

Figure 1 - Life Cycle Cost (LCC) variations versus duct diameter for 150cfm, 200cfm, and 300cfm.


Figure 2 is the same plot as Figure 1 showing the LCC versus duct diameter with additional details showing the lifetime energy cost and duct installation cost. Lifetime energy cost for fan operation increases very rapidly as duct diameter is reduced. Why? Fan power is inversely related to duct diameter raised to approximately the fifth power (actually, 4.75 power)! Heat flow through wall insulation is only inversely related to insulation thickness. A change of wall insulation thickness from 12inches to 10inches causes a 20% increase in heat flow (12/10). Reduction of duct diameter from 12inches to 10inches causes a (12/10)5 or 150% increase in fan power! And, it is important to remember that “heat” (more properly, “thermal energy”) is less valuable than a fan’s electrical energy.

Figure 2 - Same as Figure 1 but with details of lifetime energy cost and duct installation cost.

A single relation for determining the optimal duct diameter can be derived, which eliminates the necessity of evaluation a range of LCC operational costs and duct installation cost. The appendix contains the expression for the most economical duct diameter. Figure 3 shows optimal duct diameter trends over a range of air flow rates. The duct is assumed to have a 100 year lifetime and to have a 20% efficient fan-motor attached. The installation cost for duct uses a cost model described in the appendix. The appendix model assumes fixed cost per foot of installed duct plus a diameter related cost term. These two terms can be changed relative to one’s local duct installation costs. Some guidance for determining local duct installation cost factors based on quotes is included in the appendix. Also plotted on Figure 3 is air velocity (relation included in appendix). As previously mentioned, keeping residential duct velocities below 700feet per minute (fpm) is recommended. For flow ranges of most interest for residential ventilation systems, the optimal duct diameter will result in duct velocities below 700fpm.

Figure 3 - Optimum duct diameter trend versus air flow rates for a 100 year life duct system with a 20% efficient fan-motor and an installation cost of $1.65 per ft length per inch diameter of duct. Duct velocity (right hand axis) is also plotted.

Figure 4 - Optimum duct diameter curves with variations in duct lifetime, fan-motor efficiency, and duct installation cost. Duct air velocities are also plotted.

Figure 4 shows the same plot as figure 3 with some additional curves showing the impact of variations of duct lifetime, fan efficiency and installation cost. Optimum duct diameter will be reduced when the cost of energy (eg, improved fan efficiency or decreased ventilation lifetime) decreases or the cost of the duct (eg, increased duct installation cost) increases.

The Life Cycle Cost relation is proportional to changes in duct lifetime, duct installation cost and fan-motor efficiency. Doubling the cost of duct installation, doubling fan efficiency, or halving the duct lifetime all have the same impact on the optimum duct diameter. At 300cfm, the optimum duct diameter would be reduced from 12 inches to 10-11 inches in diameter if ventilation energy cost is decreased in half or the cost of duct is doubled. Note that the associated duct velocity plots included in figure 4 shows an increase from 350fpm to 450fpm at 300cfm air flow, which is below the 700fpm upper velocity recommendation.

Figure 4 shows the combined impact of more expensive duct installation with doubling of fan efficiency and decreased duct system lifetime. The combined impact of this 8-fold increase of duct cost relative to fan energy cost results in an optimum duct diameter decrease from 12 inches to 8-9 inches in diameter. This rather modest decrease in optimum duct diameter is due to the rapid rise of lifetime fan energy cost at small duct diameters. Note that air velocity for the case of 8-fold increase in duct cost to energy cost has now exceeded 700fpm. One should increase duct size to keep velocity below 700fpm in order reduce the potential for duct noise generation and transmission. Today’s high performance homes are much quieter than yesteryear’s poorly insulated and leaky homes, making duct noise transmission more of a concern.


Multi-Branch Duct Systems Cost:

The optimal duct size can be applied to any section of duct. Main duct trunk and branches are optimized individually. Note that we are not replacing the need to formally work through a duct design process such as Manual D which includes the impact of filters, grills, elbows, tees, etc. Our goal is to provide a means for determining the cost and economics of a ventilation system.

As an example, suppose a duct supply network consists of a central trunk with 300cfm that runs for 50 feet, with five 15ft long branches that separate from the central supply trunk. Four of the branches supply 50cfm while the fifth is designed to supply 100cfm. From Figure 3, we find optimum diameters for the 300cfm, 100cfm and 50cfm duct sections are 12 inches, 7 inches and 5 inches, respectively. Table 1 shows other duct system parameters for this example using relations from the appendix in a spreadsheet.

Assumptions built into Figure 3 include an assumed duct lifetime of 100years, energy cost of $0.12 per kWh, duct installation cost using information in the appendix, and fan efficiency of 20%.

The pressure drop (DP) in each branch must be balanced just as in real duct systems. That is, in Table 1, the 100cfm branch shows a pressure drop of 0.007”H2O while the 50cfm branches show a pressure drop of 0.010” H2O. Nature will equalize the pressure drop of these branches. Equalization of the pressure drop in the branches can be achieved in different manners. Adjustable grills and diffusers can be used to “balance” the branches to desired airflows, coupled with fan speed changes to achieve the overall desired flow rate. We will discuss these techniques in Ductology Part 2 when duct system performance is covered.

For the present example, we will assume that no adjustable grills or diffusers are attached to the branches. Ideally, one would like to have a “naturally” balanced duct system because any pressure increasing adjustment of a duct outlet is an addition of pressure drop, and pressure drop means fan power, and fan power costs energy and money! Table 2 shows the natural balance of the duct system. The 300cfm of the main branch is held constant (but its flow can also vary depending on the fan’s control characteristics). Adjustments are made to the branches until all branches have the same pressure drop (0.009”H2O). All branch airflows must add to the total flow through the main branch. If one finds an equal pressure drop solution for all duct branches that add to something other than 300cfm, the main duct trunk can be adjusted to this flow level. This is the basis for the “equal friction” duct sizing method. Some iteration is required as one works between balancing pressure drops and conserving air mass flow rates.

For this example, the system would naturally balance to a flow of 116cfm in the higher flow branch while the other branches are at 46cfm. In multi-branched, manifolded duct systems, accurately measuring a duct flow within 10cfm is extremely difficult, regardless of the decimal values on today’s bolometer readouts, and, regardless of whether or not the bolometer is powered compensated. Watch for more on measuring airflow in duct manifold systems in future Ductology articles. Notice that the adjusted values in Table 2 do not shift operational cost or LCC values significantly from those in Table 1, and that duct velocities are well within our desired range.

Table 3 is an example of what happens when someone “wings it” or uses “shoot-from-the hip” duct design. Decreasing the main duct branch from 12” to 8” diameter, and other duct branches to 5” (100cfm branch) and 3” (50cfm branch) results in a LCC cost increase of $2000 and fan power increase of 700%! A decrease from 12 inch to 8 inch diameter reduces the flow area to less than half, which doubles the air velocity (see Table 2 and Table 3 velocities). Because pressure drop is related to the kinetic energy of the flow, which is in turn related to the square of the velocity, one finds that the pressure drop has quadrupled! The slight savings in duct installation cost ($600) is more than offset by the cost of the fan power increase. From the perspective overall house cost, the cost of ductwork is a minor cost, especially in relation to the cost of kitchen cabinets and bathroom fixtures. The health cost of poorly designed ventilation, however, can easily exceed the cost of your home.

Table 1 – Multi-branch optimum duct diameter example.

Table 2 – Multi-branch example with optimal diameter equal friction flow adjustment.

Table 3 – Multi-branch with non-optimal duct diameter reduction (equal friction adjustment).


Small Duct Air Distribution Systems:

Multi-duct systems using small diameter ducts may allow installers more flexibility in terms of clearance space. Additionally, the plug-n-play nature of some small diameter duct systems may reduce duct installation skill, shifting ventilation system installation labor from HVAC professionals to less expensive labor.

We will explore the relative cost of a small diameter, multi-duct system using our previous multi-branch duct system example. We don’t advocate one duct system over another, but we do stress that whatever you choose, be sure that it is designed properly. Although one might find some installation cost savings with small duct systems, pressure drop sensitivity of small diameter ducts can severely limit future ventilation air flow increases.

The example schematic shows a duct distribution box (plenum) with 25 lengths (65ft) of small diameter duct for the 300cfm air flow example. Assuming the small diameter duct to have a diameter of 2.5 inches, the optimal air flow for the duct is 12cfm (see Figure 3). Remember, optimal duct diameter is independent of duct length. In order to deliver the equivalent air flow as in the previous example (~300cfm), four sets of four duct hoses are required for delivering 50cfm of air to four rooms in the home, and nine sets of duct hoses are required for delivering 100cfm of air for an approximate airflow total of 300cfm. Whereas the branched system in the previous example assume one 50ft trunk carrying 300cfm to five 15ft long distribution branches, the current example assumes 65ft duct hose lengths emanating from a single distribution box. The schematic is meant to show that this is a lot of spaghetti!

All branches have the same pressure drop if all branches are the same length. Because pressure drop is proportional to length, a ventilation system with one duct twice as long as another will also have a pressure drop that is double. If both ducts require the same airflow, the shorter duct will require some pressure drop increase with a diffuser or grill. Remember, increasing pressure drop increases fan power which increases ventilation system energy cost. Another way to compensate longer versus shorter duct hose runs is to add more duct hoses to the longer run until it has the same pressure drop as the shorter duct length, however, this adds duct installation cost.

Table 4 shows the results for the optimized small duct hose system. In comparison to Table 2 with pressure balanced (equal duct friction) branches, the small hose duct system would cost $350 less to install ($3250 vs $3600). Note that for the small duct system, the installation cost is assumed to be $2 per foot of length with no diameter related duct cost as in the larger duct installation cost model. Even though both large and small duct systems have optimized diameters, notice that the small duct system has 5 times the pressure drop per hose length as each branch in the large duct system. For the large duct system, the total pressure drop is the sum of the main duct trunk pressure drop (0.012”H2O) and the branch pressure drop (0.009”H2O) as seen in Table 2, while a 65ft long duct hose in the small diameter duct system has a pressure drop of 0.10”H2O (Table 4). The increased pressure drop in the small hose system is caused by the increased duct wall surface area. The small duct system has nearly 1100 square feet of internal duct surface area compared to 260 square feet of inside surface area for the larger duct system, which is an important duct friction factor. Overall, the small duct hose system is $1000 more expensive in Life Cycle Cost due to higher operational cost, due to higher fan power costs that offset potentially lower duct installation cost.

Finally, Table 5 shows how LCC can rapidly escalate with small duct systems if one tries to reduce installation cost by reducing the number of hoses. Reducing the number of hoses in half (note, the 9 hose branch has been reduced to a 5 hose branch) for the same overall air flow rate (~300cfm) increases the LCC by $3000 relative to Table 4 cost due to rapidly escalating fan energy cost. Table 5 LCC cost is double the optimized Table 2 large duct cost.

Table 4 - Optimal Small Duct Distribution System

Table 5 - Non-optimal, reduced small duct distribution system


Conclusion

Duct design is not fun for most people, but properly designed ventilation systems are essential for our health and for our pocketbooks. We hope Part 1 of Ductology has provided some understanding of the principles of economically optimized duct systems, and the trends associated with fan energy and duct installation costs. For sure, costs will be different in different regions of the world, but the fundamental balance of fan energy and duct installation costs are the same. The economic optimum of a duct system is that point where the rate of fan energy decrease is equal to the rate of installed duct cost increase.

Our next newsletter will examine the installed performance of duct systems. Conducting a detailed duct design as discussed in this article is the first step to ensure an economically optimized ventilation system. Ensuring that the installed duct system performs as designed is the second essential step. A simple performance test can be conducted. The results of the test will allow one to ascertain whether the installed system is properly performing. Hopefully, before the system is hidden behind wallboard.

We have avoided incorporating computational relations in the article for clarity, and even with those removed, this article is long (and boring). For those interested in the computational basis for these analyses, the appendix contains all the relations used for the figures and tables. The tables provide results that can be used to verify your calculations. And if you find errors, please let us know!


Appendix – Duct Relations

The results discussed in this article are based on standard duct friction relations. We have massaged these functions into convenient units for residential duct design, which should allow interested users to easily incorporate into a spreadsheet format.

Pressure Drop:

 DP = (1.532x10-3 x L x Q1.75 )/ D4.75
 Where
  DP = static pressure drop across duct length (“H2O)
  L = duct length (feet)
  Q = air flow (cfm, cubic feet per minute)
  D = duct diameter (inches)

As an example, an 8 inch diameter duct with 300cfm of air flowing through 100 feet of duct will have a pressure drop of 0.17”H2O. You can verify this result by checking the duct friction chart at the Engineering Toolbox.

Airflow:

If you would like to determine airflow for a given pressure drop, the reciprocal of the previous relation is:

 Q = 40.6 x (DP/L)0.57 x D2.71

Using the previous example, 100 feet of 8 inch diameter duct with 0.17”H2O pressure drop has 300cfm flow.

Power:

The power required to move air through a length of duct of a specified diameter is equal to the airflow rate times the pressure drop (P = Q x DP). The expression below includes unit conversions and fan efficiency in order to determine the fan power in terms of Watts.

 P = 1.8x10-4 x L x Q2.75 / (η x D4.75)
 Where
  P = electrical power (Watts)
  η = fan-motor efficiency (fraction)
  L = duct length (feet)
  Q = air flow (cfm, cubic feet per minute)
  D = duct diameter (inches)

For fans with airflow less than 400cfm, a good fan-motor efficiency is 0.2 (20%). Recent ASHRAE research indicates that R&D efforts could double small fan-motor efficiencies in the future (“Path to 50+% Efficient Fans For Unitary Applications”, S. Kavanaugh, D. O’Neal, ASHRAE Journal, Dec, 2017).

From the previous example, and assuming a fan-motor efficiency of 0.2, the electrical power required to have 300cfm flow through an 8 inch diameter, 100ft long duct is 30Watts. The impact of reducing duct diameter from 8 inches to 6 inches results in an increase of fan power to 118Watts! In the days of incandescent lighting, 118Watts may not sound large, but in today’s high performance homes, continuous operation of an electrical load with 118W is 1030kWh, or about $125 per year utility cost. Also note how the duct system impacts a fan’s airflow per power (cfm/W) condition. The 8 inch diameter duct results in 10cfm/W compared to a 6 inch diameter duct with 2.5cfm/W, assuming the fan’s efficiency is the same.

Duct Installation Cost:

The following is a model for installed duct cost:

 I = ( α x D2 +β x D + γ ) x L
 Where
  I = duct installation cost per length ($/ft)
  D = duct diameter (inches)
  L = duct length (ft)
  α = duct cost per diameter squared per length ($/ft-in2) ~ 0.0216$/ft-in2
  β = duct cost per diameter per length ($/ft-in) ~ 1.65$/ft-in
  γ = duct cost per length ($/ft) ~15.5$/ft

For ducts smaller than 12 inches in diameter, the higher order term (α) can be neglected. With the duct installation cost factors assumed above, the relation for duct installation cost is:

 I = ( $1.65/ft-in x D + $15.50/ft ) x L

Installation cost for a 100ft long, 8 inch diameter duct would be $2870.

Of course, this duct installation cost relation will be different based on local wage rates and material costs. These factors can be readily determined from quotations received from local contractors. One should request at installation costs for two different duct diameters. For example, suppose a home will have 75ft of duct length, and the installation quote for 8 inch diameter duct is $2500 and the quote for 10 inch diameter duct is $3000.

The β factor for duct installation would be determined as:

 β = ($3000 – $2500)/((10in – 8in)x75ft) = $3.33/ft-in

and the γ factor would be:

 γ = ($3000/75ft) – ($3.33/ft-in) x 10in = $6.7/ft

The β factor is important for determining the optimal duct diameter, discussed later.

Lifetime Energy Cost:

The lifetime energy cost for operation of a fan for blowing air through a length of duct is:

 E = 1.8x10-7 x L x Q2.75 x t x U / (η x D4.75)
 Where
  E = lifetime energy cost ($)
  L = duct length (ft)
  Q = air flow (cfm)
  t = duct lifetime (years; eg, 100 years)
  U = utility energy cost ($/kWh; eg, $0.12/kWh)
  η = fan-motor efficiency (eg, 0.2)
  D = duct diameter (inches)

Life Cycle Cost (LCC) Relation:

The LCC based on the previous duct relations, and assuming negligible time value of money is the sum of lifetime duct operation cost and duct installation cost.

 LCC = E + I
 Where
  LCC = life cycle cost ($)
  E = lifetime energy cost ($)
  I = duct installation cost ($)

Optimum Duct Diameter:

An expression for the most economical duct diameter can be derived from the LCC relation. The optimum diameter is the one that minimizes the LCC relation, that is, minimies the sum of lifetime energy cost and installation cost.

  Dopt = [(8.55x10-7 x Q2.75 x t x U)/( η x β)]0.174
  Where
  Dopt = optimum duct diameter (inches)
   Q = air flow (cfm)
   t = duct lifetime (years)
   U = utility energy cost ($/kWh)
   η = fan-motor efficiency
   β = duct installation cost parameter ($/ft-in)

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Mar 28, 2022 Featured Article – Introducing Victor Niño as Build Equinox Director of Business Development 20220328
Feb 22, 2022 Tech Announcement – We’re Particular About Particulates! Tags: Particulates 20220222
Feb 22, 2022 Featured Article – Exciting New CERV2 Features and Options! Tags: CERV 20220222
Jan 27, 2022 Featured Article – Efficient, Smart Bathroom Ventilation with the CERV2 Tags: Bathroom 20220127
Jan 27, 2022 Review – Attending Large Venue Events – Go Illini, beat COVID! 20220127
Jan 27, 2022 Spotlight – Vermod in the News! 20220127
Dec 22, 2021 Featured Article – Filters are More Important (and Expensive) than Energy! Tags: Filters, Particulates 20211222
Dec 22, 2021 Spotlight – Sneak Peak: TBDA Decarbonization Project 20211222
Nov 15, 2021 Events – Two Talks in One Night at ASHRAE Madison (Dec. 13, 2021, CEUs available!) Tags: Webinar 20211115
Nov 15, 2021 Featured Article – Taylor CERV2+Ducted Mini Install (2.5 Year Follow-up) Tags: CERV, Renovation 20211115
Oct 25, 2021 Events – PHMass Passive House Virtual Symposium (Nov 3, 2021) Tags: Passive House, Webinar 20211025
Oct 25, 2021 Review – The Role of Global Air Pollution in Aging and Disease, by Professor Caleb Finch Tags: Health 20211025
Oct 25, 2021 Featured Article – Sustainable Schools Create a Sustainable Future Tags: CERV 1000 20211025
Sep 30, 2021 Events – PHIUScon 2021 Presentation: Human Centric Metrics for Improving Health, Comfort and Productivity Tags: Conference, Passive House 20210930
Sep 30, 2021 Featured Article – Kitchens are Exhausting! Tags: Kitchen 20210930
Sep 29, 2021 Events – Virtual Metro Denver Green Homes Tour 20210929
Aug 17, 2021 Opinion Article – ASHRAE, You’re Making Us Sick! Tags: ASHRAE 20210817
Aug 17, 2021 Featured Article – CERV2 Smart, Integrated, Supercharged Dehumidification Tags: CERV, Dehumidification 20210817
Jul 19, 2021 Events – CERV2 Smart-er Ventilation New Features & Product Demo (Video & Slides) Tags: CERV 20210719
Jul 19, 2021 Review – 5 Steps to Net Zero Multi-family Residence Renovation: Toronto Tags: Renovation 20210719
Jul 19, 2021 Featured Article – Test Chamber Pt. 2: VOCs! Tags: VOC 20210719
May 20, 2021 Tech – It’s Springtime and Aprilaire is in the Air! Tags: Dehumidification 20210520
May 18, 2021 Featured Article – Alexa, Meet the CERV 20210518
Apr 19, 2021 Spotlight – Illinois ADAPTHAUS Wins 1st Place in Comfort & Environmental Quality Tags: Comfort, Indoor Air Quality, Solar Decathlon 20210419
Apr 19, 2021 Events – Register for Building Energy Boston (Online)! May 5-7 Tags: Conference, Webinar 20210419
Apr 19, 2021 Featured Article – Broken Clocks Work Better than Today’s Ventilation Standards Tags: ASHRAE, Indoor Air Quality 20210419
Apr 19, 2021 Events – Upcoming Online Webinars and Conferences! Tags: Conference, Webinar 20210419
Mar 11, 2021 News – New Video, Booklet, and CERV2 Smart Options! Tags: CERV 20210311
Mar 10, 2021 Spotlight – CERV Installed in the UofI ADAPTHAUS Tags: CERV, Solar Decathlon 20210310
Mar 10, 2021 Events – Re-Opening Schools and Beyond Safely Webinars (3/23, 4/21, 4/22) Tags: Webinar 20210310
Mar 10, 2021 Featured Article – Human Value: Thinking Beyond Energy Tags: Energy Efficiency, Health 20210310
Feb 26, 2021 Spotlight – Dar-Lon Chan’s Journey to Sustainable Living 20210226
Feb 26, 2021 Featured Article – Covid Safe Space Calculator Tags: Health 20210226
Jan 29, 2021 Events – Efficiency Vermont Better Buildings by Design Conference (Feb 2-4) Tags: Conference 20210129
Jan 29, 2021 Spotlight – University of Illinois ADAPTHAUS becoming Reality Tags: Solar Decathlon 20210129
Jan 29, 2021 Featured Article – CERV2 Installed in Equinox House! Tags: CERV, Equinox House 20210129
Dec 21, 2020 Spotlight – Tour Bill Spohn’s New Modular Net Zero Home (CEUs available!) Tags: CERV, New Construction 20201221
Dec 21, 2020 Special Edition – Ventilation, Vaccination, Infection, and Luck. Covid-19 and the New Year Tags: Health 20201221
Dec 21, 2020 Featured Article – AWE: Air, Water, Energy Tags: Energy Efficiency, Indoor Air Quality, Water 20201221
Nov 17, 2020 Events – CERV2 Smart-er Ventilation Product Demo (Video + PDF) Tags: CERV, Webinar 20201117
Nov 16, 2020 Spotlight – New Lungs for a 101-Year-Old Home Pt.3: Heat Pump Water Heater! Tags: Renovation, Water 20201116
Nov 15, 2020 Featured Article – Equinox Meets the Needs / ASHRAE Solar ZEB Article 12 Tags: ASHRAE, Equinox House 20201115
Nov 12, 2020 Special Edition – Stay Safe this Holiday Season! Tags: Health 20201112
Oct 29, 2020 Spotlight – New Lungs for a 101-Year-Old Home Pt.2: Total HVAC Replacement! Tags: CERV, Comfort, Heat Pump, Renovation 20201029
Oct 28, 2020 Featured Article – Equinox House Performance / ASHRAE Solar ZEB Article 10 Tags: ASHRAE, Equinox House 20201028
Sep 22, 2020 Events – Michigan Residential Net Zero Energy Conference (Oct 20-22) Tags: Conference 20200922
Sep 22, 2020 News – CERV-UV Now Available for New Orders! Tags: CERV, UV 20200922
Sep 22, 2020 News – CERV-ICE Now in the iOS and Android App Stores! Tags: CERV 20200922
Sep 22, 2020 Featured Article – Solar Collection & Use / ASHRAE Solar ZEB Article 10 Tags: ASHRAE, Equinox House, Solar 20200922
Aug 17, 2020 Special Edition – Build Equinox Groundbreaking Research into COVID 19 Tags: Health 20200817
Aug 17, 2020 Events – SEDAC Webinar: Considerations, Best Practices, and Energy Implications for Reopening Critical Community Facilities in the Pandemic (Aug 18, 2020) Tags: Webinar 20200817
Aug 17, 2020 Featured Article – Comfort Conditioning & Indoor Air Quality / ASHRAE Solar ZEB Article 9 Tags: ASHRAE, Comfort, Equinox House, Indoor Air Quality 20200817
Aug 17, 2020 News – Building Science Podcast: “Ventilation & Virus Transmission Prevention” Tags: Health, Webinar 20200817
Aug 14, 2020 News – New HVAC School Podcast: “Advanced Ventilation w/ CERV2” (Watch/Listen) Tags: CERV, Webinar 20200814
Aug 12, 2020 Events – Free CEU Webinar: Can Building Science Help Us Slow COVID-19? (Sep 2, 2020) Tags: Health, Webinar 20200812
Jul 10, 2020 Special Edition – Covid-19 Update: Airborne Means AIRBORNE! Tags: Health 20200710
Jul 10, 2020 Featured Article – Appliances Power EVs / ASHRAE Solar ZEB Article 8 Tags: ASHRAE, Energy Efficiency, Equinox House 20200710
Jun 29, 2020 Events – Free New Webinar: Guidelines for Protecting Against COVID-19 (PDF + Slides) Tags: Health, Webinar 20200629
Jun 25, 2020 Featured Article – Designing a Thermally Massive Home/ASHRAE Solar ZEB Article 7 Tags: ASHRAE, Equinox House 20200625
Jun 25, 2020 Special Edition – Covid19 Status Report: We are at the Beginning of the Pandemic, Not the End Tags: Health 20200625
May 29, 2020 Spotlight – CERV Retrofit: New Lungs for a 101-Year-Old Home Tags: CERV, Renovation 20200529
May 29, 2020 Special Edition – Covid19 Status Report: Guidelines for Homes & Businesses Tags: Health 20200529
May 29, 2020 Featured Article – Ground Heat Transfer/ASHRAE Solar ZEB Article 6 Tags: ASHRAE, Equinox House 20200529
Apr 16, 2020 Events – Free CEU Webinar: Covid-19 Characteristics, Transmission, and Control (April 29th) Tags: Health, Webinar 20200416
Apr 16, 2020 Special Edition – Battling the Spread of Covid-19 Tags: Health, Report 20200416
Apr 16, 2020 Featured Article – Infiltration & Sealing/ASHRAE Solar ZEB Article 5 Tags: Energy Efficiency, Equinox House, Net Zero, Report 20200416
Apr 16, 2020 Spotlight – New Projects: 1930s CERV Retrofit & Mitsubishi Hyperheat Tags: CERV, Energy Efficiency, Heat Pump, Ventilation 20200416
Mar 13, 2020 Featured Article – Light and Delight/ASHRAE Solar ZEB Article 4 Tags: Comfort, Energy Efficiency, Equinox House, Solar 20200313
Mar 10, 2020 News – CERV Voted One of the Top 16 Coolest Things Made in Illinois! Tags: CERV 20200310
Mar 5, 2020 Special Edition – Fighting COVID-19 with Fresh Air Tags: Health, Indoor Air Quality, Report, Ventilation 20200305
Feb 24, 2020 Featured Article – Walls and Roof/ASHRAE Solar ZEB Article 3 Tags: Equinox House, Net Zero, Report, ZEROs 20200224
Feb 24, 2020 Tech – Magic-Box Mechanicals Tags: CERV, Comfort, Heat Pump, Ventilation 20200224
Feb 24, 2020 Events – Designing Exceptional Homes for Exceptional People Webinar (Video + PDF) Tags: Comfort, Energy Efficiency, Net Zero, Webinar, ZEROs 20200224
Jan 30, 2020 Events – Visit us (Booth 17) at Energy Design Expo in Duluth (2/25-26) Tags: CERV 20200130
Jan 14, 2020 Tech – Designing Exceptional Homes for Exceptional People Tags: Comfort, Ducting, Humidity, Indoor Air Quality, Report, Ventilation, ZEROs 20200114
Jan 14, 2020 Featured Article – Designing for Zero/ASHRAE Solar ZEB Article 2 Tags: Energy Efficiency, Equinox House, Net Zero, Report, Solar, ZEROs 20200114
Dec 19, 2019 Events – Free Webinar: Smart Ventilation & Air Distribution (Video+PDF) Tags: Ducting, Ventilation, Webinar 20191219
Dec 19, 2019 Events – CERV2 Smart-er Ventilation Product Demo (Video + PDF) Tags: CERV, Webinar 20191219
Dec 19, 2019 Spotlight – Acorn Glade: 2019 NAPHC Awardee! Tags: CERV, Net Zero, Passive House, Solar 20191219
Dec 16, 2019 Featured Article – Equinox Origins/ASHRAE Solar ZEB Article 1 Tags: Equinox House, Report 20191216
Nov 19, 2019 Events – Visit our booth at 2019 NAPHC in Washington DC! Tags: Passive House 20191119
Nov 19, 2019 Spotlight – Equinox House Turning 10! Tags: Equinox House 20191119
Nov 19, 2019 Featured Article – Handling Humidity Pt.4 Putting it All Together Tags: Humidity, Report, Ventilation, ZEROs 20191119
Oct 16, 2019 Events – Mechanical Systems for Passive Buildings (Chicago, Oct 16) Tags: CERV 20191016
Oct 16, 2019 Featured Article – Handling Humidity Pt.3 Methods for Managing Moisture Tags: Comfort, Humidity, Indoor Air Quality, Ventilation 20191016
Oct 16, 2019 Events – Free Webinar: Handling Humidity (Video + PDF) Tags: Comfort, Humidity, Indoor Air Quality, Ventilation, Webinar 20191016
Oct 16, 2019 Events – Free CEUs: Building Green & Beer at Founders Brewing (Oct 28) 20191016
Oct 16, 2019 Spotlight – Inter House Wins Solar Decathlon Africa!!! Tags: CERV, Net Zero, Solar 20191016
Sep 20, 2019 Featured Article – Handling Humidity Pt.2 Climate Moisture Variations Tags: Comfort, Humidity, Ventilation, ZEROs 20190920
Sep 20, 2019 News – Brand New Release: Colorfil VOC Absorbing Filters! Tags: CERV, Filters, Health, Indoor Air Quality, Ventilation 20190920
Sep 20, 2019 Tech – From CERV to CERVEZA: a Quest for Smart Beer Tags: CERV, Heat Pump 20190920
Aug 27, 2019 Events – Earn Free CEUs with the Handling Humidity Webinar (Aug 29) Tags: Comfort, Humidity, Ventilation, ZEROs 20190827
Aug 27, 2019 Featured Article – Handling Humidity Report Series Tags: Comfort, Humidity, Ventilation, ZEROs 20190827
Aug 12, 2019 News – Listen to the Building HVAC Science Podcast, ft. Ty Newell! Tags: CERV, Comfort, Health, Indoor Air Quality, Webinar 20190812
Jul 29, 2019 Events – CERV2 Smart-er Ventilation Product Demo (Aug 27, 2019) Tags: CERV, Heat Pump, Ventilation 20190729
Jul 29, 2019 Featured Article – Poor Home Maintenance = Increased Health Risks Tags: Comfort, Ducting, Energy Efficiency, Health, Humidity, Ventilation 20190729
Jul 29, 2019 Tech – Say Hello to Our New Server! 20190729
Jun 19, 2019 Featured Article – Watch out for Cranky Heaters! Tags: Energy Efficiency, Heat Pump 20190619
Jun 19, 2019 Events – Free CEU Webinar: Smart Ventilation & Air Distribution (July 10) Tags: CERV, Ducting, Energy Efficiency, Indoor Air Quality, Ventilation 20190619
Jun 19, 2019 Spotlight – Marrakech Express! CERV2 Heading to Africa! Tags: CERV, Net Zero, Solar 20190619
May 13, 2019 Featured Article – Taylor Home CERV Testimonial Tags: CERV, Comfort, Indoor Air Quality, Ventilation 20190513
May 13, 2019 Events – 7 Steps for Designing an Economical Net Zero Home (Video + PDF) Tags: Energy Efficiency, Net Zero, Solar, Ventilation, Water, Webinar, ZEROs 20190513
May 13, 2019 Tech – AeroBarrier Demonstration Tags: Energy Efficiency, Ventilation 20190513
Apr 15, 2019 Events – Indoor Air Quality Metrics Free Webinar (Apr 24, 2019) Tags: Comfort, Health, Indoor Air Quality 20190415
Apr 15, 2019 Featured Article – CERV2 Geo–Boost Tags: CERV, Energy Efficiency 20190415
Apr 15, 2019 Review – 2019 National Home Performance Conference Tags: Indoor Air Quality 20190415
Apr 15, 2019 Tech – CERV2 Sketchup Model Now Available Tags: CERV 20190415
Mar 28, 2019 News – Visit us at the Chicago 2019 National Home Performance Conference Tags: CERV 20190328
Mar 28, 2019 Featured Article – Happy Equinox, St. Patrick’s Day, and Super Moon! Tags: Equinox House 20190328
Feb 27, 2019 Events – Free CEU Webinar: Smart Ventilation & Air Distribution (Mar 12) Tags: CERV, Ducting, Energy Efficiency, Indoor Air Quality, Ventilation, Webinar 20190227
Feb 27, 2019 Featured Article – Smart Ventilation and Smart Air Distribution Reports Tags: CERV, Ducting, Energy Efficiency, Indoor Air Quality, Ventilation 20190227
Feb 27, 2019 Spotlight – El Salvador NZEB Update Tags: CERV, Net Zero, Solar 20190227
Feb 25, 2019 Events – CERV2 Smart-er Ventilation Product Demo (Video + PDF) Tags: CERV, Heat Pump, Indoor Air Quality, Ventilation, Webinar 20190225
Jan 22, 2019 Events – Smart Ventilation & Smart Air Distribution Webinar (Video & PDF) Tags: CERV, Ducting, Energy Efficiency, Indoor Air Quality, Ventilation, Webinar 20190122
Dec 26, 2018 Spotlight – Progressive Canada Tags: CERV, Net Zero, Passive House, Solar 20181226
Dec 26, 2018 News – Happy Holidays from Build Equinox! 20181226
Dec 26, 2018 Review – CERV2 at Greenbuild 2018 Tags: CERV 20181226
Nov 26, 2018 News – CERV OEM Filter Store is OPEN!!! Tags: CERV, Indoor Air Quality 20181126
Nov 19, 2018 News – Check Out Our Social Media! 20181119
Oct 24, 2018 Events – Free CEU Webinar: Duct Design & Performance (PDF Download) Tags: Ducting, Energy Efficiency, Webinar 20181024
Oct 24, 2018 Featured Article – CERV2 is UL Approved! Tags: CERV 20181024
Oct 24, 2018 News – Stop by Our Booth at Greenbuild Chicago (Free Tickets!) Tags: CERV 20181024
Oct 24, 2018 Spotlight – University of Illinois Students Visit Build Equinox Tags: CERV 20181024
Jul 23, 2018 Featured Article – Happy 10th Birthday, CERV and Sunflower! Tags: CERV, Solar 20180723
Jul 23, 2018 Spotlight – Good News from El Salvador! Tags: CERV, Net Zero, Solar 20180723
Jun 22, 2018 Tech – Installing a Ductless Mini-split Tags: Heat Pump 20180622
Jun 22, 2018 Featured Article – Mini-split Mania! Tags: Heat Pump 20180622
Apr 30, 2018 News – Now offering on-demand webinars for CEUs! 20180430
Apr 30, 2018 Events – Free CEU Webinar! (May 2, 2018) 20180430
Apr 30, 2018 Featured Article – Ductology Part 2 Tags: Ducting, Report, Ventilation 20180430
Feb 19, 2018 Review – 2018 Better Buildings by Design Conference, Flu and Colds 20180219
Feb 19, 2018 Featured Article – Hot Water! Tags: Comfort, Water 20180219
Jan 22, 2018 Events – Visit us at BuildingEnergy Boston! (March 7-9, Boston, MA) 20180122
Jan 22, 2018 Events – Efficiency Vermont Better Buildings by Design Conference (Feb 7-8) 20180122
Jan 22, 2018 Featured Article – Ductology (Part 1) Tags: Ducting, Report, Ventilation 20180122
Nov 20, 2017 Featured Article – Heat Pump (Hybrid) Clothes Dryers are Coming! Tags: Heat Pump 20171120
Oct 31, 2017 Featured Article – CERV2 Measures IAQ at NAPHC & NAPHN 20171031
Sep 25, 2017 Featured Article – Introducing CERV2 Tags: CERV 20170925
Aug 21, 2017 Events – Free CEU Webinar! (Sep 27, 2017) 20170821
Aug 21, 2017 Featured Article – Quiz 20170821
Jul 27, 2017 Events – New IAQ Metrics Webinar (Video + PDF) Tags: Health, Indoor Air Quality, Ventilation 20170727
Jul 25, 2017 Featured Article – Endotoxins: Small But Very Significant Tags: Health, Indoor Air Quality, Report, Ventilation 20170725
May 22, 2017 Events – Economical Net Zero Design Webinar (Video+PDF) Tags: Energy Efficiency, Net Zero, Webinar, ZEROs 20170522
May 22, 2017 Featured Article – Styrax Japonicus 20170522
Apr 28, 2017 Events – 7 Steps for Designing an Economical Net Zero Home (May 25) Tags: Energy Efficiency, Net Zero, Webinar, ZEROs 20170428
Apr 28, 2017 Featured Article – Engineering Net Zero Homes Tags: Net Zero, ZEROs 20170428
Mar 20, 2017 Featured Article – Build Equinox Zero Plus Facility Tags: Energy Efficiency, Net Zero, Solar 20170320
Feb 14, 2017 Featured Article – February Flu Tags: Health, Indoor Air Quality, Report, Ventilation 20170214
Jan 20, 2017 Events – HRV, ERV and Smart Vent Systems, Free CEU Webinar (Feb 15) Tags: CERV, Energy Efficiency, Ventilation, Webinar 20170120
Jan 20, 2017 Events – NESEA IAQ Metrics Presentation (Mar 9, Boston, MA) Tags: Health, Indoor Air Quality 20170120
Jan 19, 2017 Featured Article – The Perfect Dust Storm Tags: Health, Indoor Air Quality, Report, Ventilation 20170119
Jan 12, 2017 Events – Efficiency Vermont Better Buildings by Design Conference (Feb 1-2) Tags: CERV 20170112
Dec 26, 2016 Featured Article – Happy Holidays from Build Equinox! 20161226
Nov 29, 2016 Featured Article – Geo-Boost Tags: CERV, Energy Efficiency 20161129
Nov 29, 2016 Spotlight – This Old Passive House Tags: Energy Efficiency, Passive House, Ventilation 20161129
Nov 29, 2016 Review – House Music 20161129
Oct 28, 2016 Featured Article – Comparing ERV, HRV, and CERV Tags: CERV, Energy Efficiency, Heat Pump, Ventilation 20161028
Oct 28, 2016 Spotlight – Net Zero Eco-House (Monticello, IL) Tags: CERV, Energy Efficiency, Net Zero, Passive House 20161028
Oct 28, 2016 Spotlight – Forty Under 40 20161028
Sep 28, 2016 Events – Free CEU Webinar (Oct 5th): Why are new Indoor Air Quality metrics needed? Tags: Health, Indoor Air Quality, Ventilation 20160928
Sep 28, 2016 Review – 2016 North American Passive House Conference Tags: Passive House 20160928
Sep 28, 2016 Featured Article – New CERV-ICE IAQ Analytics Released! Tags: CERV, Health, Indoor Air Quality 20160928
Sep 28, 2016 Spotlight – CERVs in Passive Homes, pt. 2 Tags: CERV, Passive House 20160928
Aug 18, 2016 Featured Article – Understanding the House as a System Tags: Comfort, Energy Efficiency, Humidity, Indoor Air Quality, Net Zero, Ventilation 20160818
Aug 18, 2016 Spotlight – CERVs in Passive Homes Tags: CERV, Passive House 20160818
Aug 18, 2016 Review – “What is IAQ?”, P. Ole Fanger Tags: Indoor Air Quality 20160818
Aug 18, 2016 Tech – CERV CO2/VOC Library Tags: CERV, CO2, Health, Indoor Air Quality, Report, VOC 20160818
Jul 19, 2016 Events – September North American Passive House Conference Tags: Passive House 20160719
Jul 18, 2016 News – CERV Website Tags: CERV 20160718
Jul 18, 2016 Featured Article – VERMOD CERV Report Released Tags: CERV, Energy Efficiency, Indoor Air Quality, Report 20160718
Jul 18, 2016 Review – LBNL report: “Houses are Dumb Without Smart Ventilation” Tags: Indoor Air Quality, Report, Ventilation 20160718
Jul 18, 2016 Spotlight – Professor P. Ole Fanger (1934-2006); IAQ and Comfort Pioneer Tags: Comfort, Indoor Air Quality 20160718
Jul 18, 2016 Tech Note – Airflow Calculation for Ventilation Systems Tags: Ducting, Report, Ventilation 20160718

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