Posts Tagged ‘Residential ventilation’

Angry Air!

June 7, 2017

John Tooley said, “Air is like crooked rivers, crooked people, teenagers, and cheap labor.  It always seeks the path of least resistance.”  He didn’t say that Angry air is Noisy air.   Air doesn’t like being forced through corrugated, flexible ducting, pushed around corners, and made to force open dampers.  It resists being made to perform in a way that it doesn’t want to.  It takes more and more force as the resistance increases.  Air is just fine when you just let it move at will.  It can become amazingly strong as any building that has met a hurricane or tornado can attest to.  And as objects like asteroids and space capsules hurtle through the atmosphere they burn up!

ASHRAE 62.2 requires bathroom fans to make no more noise than a quiet refrigerator in a quiet kitchen: 1 sone or less.  And if you put an Energy Star bathroom fan on the bench and plug it in, you can barely hear it.  It’s amazingly quiet.  “Is it running?” people ask.  And it is.  So how come once you install the fan in the ceiling it gets uncomfortably loud?

Fan manufacturers not only made these fans quiet, they put DC motors in them that are extremely tolerant ofchanges in pressure.  As the pressure increases in the installation, the fan motor compensates by using more power to increase the speed of the spinning wheel that is pushing the air.  (Notice the curve on this graph that starts on on the left side and then drops off the cliff at about 75 cfm.  It has about the same airflow from 0.45 iwg as it does at 0.0 iwg!)  That’s a wonderful thing because people can install the fans horribly and step on the duct and lots of other nasty things and still come out with the same airflow . . . but not the same sound level.  What was really, really quiet is now uncomfortably loud.  And as houses get tighter they get quieter and a noisy fan is annoying which is why so much effort was made to get them quiet so they could run all the time without bothering anyone!

I have found that builders get aggravated because these quiet and expensive fans that they have been compelled to install really aren’t all that quiet.  And they should be quiet.  They have been designed to be quiet.  Tested to be quiet.  And if you disconnect them from the installation, they are quiet.

So here’s a simple way to determine if the fan is working right: listen to it.  If the air is angry, it will be noisy and noisy DC fans equal bad installation.  The air is yelling at you.  I have found ducts filled with the foam that was sprayed on the house for insulation.  Backdraft dampers remain taped closed.  Ducts terminated against a wall or floor in the attic and don’t actually get to the outside.  If a bathroom fan that is rated to be < 0.3 sones is noisy, its a bad installation.  Period.  Fix it.  It may still be moving enough air to meet the ventilation requirements, but if it is noisy the homeowner will find a way to turn it off and stuff it full of socks.  Then the air in the house will get bad and people will get sick.  And the occupants will get angrier than the air!  And the really dumb thing is that all these codes and standards and mathematical computations and formulas to size the fan correctly mean absolutely nothing if the fan is turned off.

What do you know about your house’s nose?

January 19, 2017

What’s special about an exterior vent hood or cap or (if you want to be technical) termination fitting?  That’s like asking what’s special about a nose?  Without vent caps the air would not leave the house in an orderly fashion.  Just like the air coming out of your lungs.  When your nose is stopped up, it’s hard to breathe.  The same is true with a vent cap.  If a dryer vent cap is full of lint, the air has a hard time getting out of the dryer.  And that’s a shame because it is the movement of air that allows the clothes to dry.  Lint traps don’t always work very well despite the enthusiasm that dryer manufacturers have for them.

wc-series-wall-cap-building-envelope-rainscreen-225x225But I want to tell you about a very special wall cap made by Primex.  This one is meant to be connected to 4″ ducting.  Nothing really special there.  So what is special?  Well, for one thing the 4″ duct is meant to slide inside the throat on this fitting.  As duct pieces are fitted together, the first piece is meant to fit inside the second piece, the second piece inside the third and so on.  Why?  Because if the first piece fits outside the second piece, any gaps or cracks will spill air outside the duct because the pressure is on the upstream side.

What else is special about this vent cap?  The mounting flange and the outside collar are all made of one piece so water can’t come in.  And yet the hood itself can be unscrewed from the flange for cleaning and service.  The flange can remain permanently attached to the wall!

It also has an very good, gravity return back-draft damper and bird screen both of which can be removed (the damper snaps out, the screen has to be cut out).

But the best part is the curve of the hood itself.  This curve gently eases the air out of the end of the duct.  A lot of caps have very abrupt exits and that increases the resistance.  Resistance in these products can be simulated by the number of equivalent feet of straight,

p1000260

Poor Quality Vent Caps

rigid ducting.  Some hoods can have equivalent lengths of 60 or 70 feet!  This hood has an equivalent length of just 25 feet.  Air has to trundle along the duct, bounce around corners, and rattle away over the corrugations of flex duct.  And when at last it gets to the termination fitting, it is compelled to make one last turn while pushing open the damper and then exit to freedom!  You want to make that as easy as possible.

Oh, one more thing . . . two more things: the cap is made of durable UV-protected polymer resin that lasts a really long time and, two,  it comes in a multitude of colors – white, taupe, black, light gray, tan, and (on special order) dark gray and dark brown.

Think about it. PRMX-WC401

Should a homeowner have control of the ventilation system?

January 25, 2014
Brightened Circuit 2

Sophisticated Control

Allison Bailes started this discussion on his Energy Vanguard site.  (Go to http://bit.ly/LRL43Q)  I was going to respond there, but there wasn’t enough room.  I used to build sophisticated controls that would do all sorts of wonderful things, but they got complicated and expensive.

You can feel the heat from a heating system.  You can feel the coolth from the air conditioning system.  You can see the change in daylight and know when you should turn on the electric light.  You can’t see or smell radon or carbon monoxide or PM 2.5 particles.

Heat is needed when it’s cold.  Cooling is needed when it’s hot.  Ventilation is needed . . . when?  When the bathroom is smelly?  When the bacon burns?  There is no one, single marker or flag for mechanical ventilation.  If there was, it would be simple to answer the question, “Should a homeowner have control of the ventilation system?”

So if a homeowner is going to control his or her ventilation system, how would he or she do it?  Manual control through an on/off switch perhaps coupled to a light in a bathroom?  This approach is equivalent to an occupancy sensor.  I did some tests of ventilation controls a number of years ago, and a manual control like that had exactly the same impact on the humidity in the bathroom as having no fan at all.  No impact.  Might as well not have a bath fan as far as humidity is concerned if you’re going to control it with a light switch.  It might have some impact on methane, but I don’t have the data on that.

Manual ventilation control will not work well because we can’t tell people when they should turn the fan on and when they should turn it off.  And when (or if) they ever turn it on again.

So that leaves the alternative of automatic control.

A standard humidity control will turn the fan on when the humidity rises above the set point.  What’s the set point? 70% RH (like 70 degrees F)?  55% or 30%?  Do you change the set point seasonally?  Do you change it on the same days every year like the change in daylight savings time (or putting fresh batteries in the smoke detectors)?  Will the fan run all the time in hot humid weather?  In my control tests, a humidity control that was set to turn the fan on at 43% RH and off at 41% RH ran for 20 minutes on the day that I tested it.  If I had set it to turn on at 41% RH and off at 38% RH on the same day, it would have run for 9 hours.  Relative humidity is difficult to explain under any conditions, but constantly adjusting the RH set point is not an effective way to control the ventilation system.

CO2 might be good for occupancy, but it is certainly not the only reason to ventilate a house.  I built a ventilation control that used a mixed gas sensor.  We called the “Flatustat”.  Works great.  The one in my bathroom has been operational for the past 20 years or so.  We could create a control that responded to a any number of IAQ conditions, but they would be expensive, and it is difficult enough to get people just to invest in mechanical ventilation in the first place.  Price is definitely a barrier.

So how about quasi-occupant control with a timer?  How should it be set?  The ASHRAE 62.2-2013 Standard says that if you’re going to run the fan half the time you need twice the airflow.  If you’re going to run the fan one third of the time, you need three times the airflow.  If you’re going to go beyond a three hour on/off period, you’re going to need to do some more calculations which depends on the ventilation effectiveness and air turnover and the fan gets really big.

But why do that?  The energy saved for most systems by shutting them off for part of an hour or even three hours, is small.  You could save energy by shutting off your clock when you weren’t looking at it. You could save energy by shutting off your doorbell when you weren’t expecting company.  Doorbell transformers use power just sitting there.

So why not just size the fan to meet the 62.2-2013 Standard and let it run all the time?  There is some weird psychological barrier to this really simple, basic, least expensive and logical solution.  The Standard says you have to give the occupant control so they can shut it off.  It’s their house.  They should be able to shut things off that they don’t want running, but there probably should be a sign warning of the consequences if they do that.

Someone once told me that the first thing many people do when they walk in the door of their home is to turn the TV on.  Maybe the ventilation system should be controlled by the same switch.  Turn on the TV.  Turn on the ventilation system.  I’m glad that wouldn’t work for everybody.

You could think about the ventilation system as a scuba tank.  When you’re under water, you wouldn’t want to shut your air off for any period of time.  When you’re in a house (a contained volume of air that is continuously being polluted by waste air from people and possessions), you’re effectively under water.  Don’t shut off your air.  Keep it simple.  Take a deep breath.  It’s okay to let it run.

Check out our website: http://www.heyokasolutions.com/

Coming soon: Average and Effective Air Change Rates: One Limburger at a Time

Should a homeowner have control of the ventilation system?

January 24, 2014
Brightened Circuit 2

Sophisticated Control

Allison Bailes started this discussion on his Energy Vanguard site.  (Go to http://bit.ly/LRL43Q)  I was going to respond there, but there wasn’t enough room.  I used to build sophisticated controls that would do all sorts of wonderful things, but they got complicated and expensive.

You can feel the heat from a heating system.  You can feel the coolth from the air conditioning system.  You can see the change in daylight and know when you should turn on the electric light.  You can’t see or smell radon or carbon monoxide or PM 2.5 particles.

Heat is needed when it’s cold.  Cooling is needed when it’s hot.  Ventilation is needed . . . when?  When the bathroom is smelly?  When the bacon burns?  There is no one, single marker or flag for mechanical ventilation.  If there was, it would be simple to answer the question, “Should a homeowner have control of the ventilation system?”

So if a homeowner is going to control his or her ventilation system, how would he or she do it?  Manual control through an on/off switch perhaps coupled to a light in a bathroom?  This approach is equivalent to an occupancy sensor.  I did some tests of ventilation controls a number of years ago, and a manual control like that had exactly the same impact on the humidity in the bathroom as having no fan at all.  No impact.  Might as well not have a bath fan as far as humidity is concerned if you’re going to control it with a light switch.  It might have some impact on methane, but I don’t have the data on that.

Manual ventilation control will not work well because we can’t tell people when they should turn the fan on and when they should turn it off.  And when (or if) they ever turn it on again.

So that leaves the alternative of automatic control.

A standard humidity control will turn the fan on when the humidity rises above the set point.  What’s the set point? 70% RH (like 70 degrees F)?  55% or 30%?  Do you change the set point seasonally?  Do you change it on the same days every year like the change in daylight savings time (or putting fresh batteries in the smoke detectors)?  Will the fan run all the time in hot humid weather?  In my control tests, a humidity control that was set to turn the fan on at 43% RH and off at 41% RH ran for 20 minutes on the day that I tested it.  If I had set it to turn on at 41% RH and off at 38% RH on the same day, it would have run for 9 hours.  Relative humidity is difficult to explain under any conditions, but constantly adjusting the RH set point is not an effective way to control the ventilation system.

CO2 might be good for occupancy, but it is certainly not the only reason to ventilate a house.  I built a ventilation control that used a mixed gas sensor.  We called the “Flatustat”.  Works great.  The one in my bathroom has been operational for the past 20 years or so.  We could create a control that responded to a any number of IAQ conditions, but they would be expensive, and it is difficult enough to get people just to invest in mechanical ventilation in the first place.  Price is definitely a barrier.

So how about quasi-occupant control with a timer?  How should it be set?  The ASHRAE 62.2-2013 Standard says that if you’re going to run the fan half the time you need twice the airflow.  If you’re going to run the fan one third of the time, you need three times the airflow.  If you’re going to go beyond a three hour on/off period, you’re going to need to do some more calculations which depends on the ventilation effectiveness and air turnover and the fan gets really big.

But why do that?  The energy saved for most systems by shutting them off for part of an hour or even three hours, is small.  You could save energy by shutting off your clock when you weren’t looking at it. You could save energy by shutting off your doorbell when you weren’t expecting company.  Doorbell transformers use power just sitting there.

So why not just size the fan to meet the 62.2-2013 Standard and let it run all the time?  There is some weird psychological barrier to this really simple, basic, least expensive and logical solution.  The Standard says you have to give the occupant control so they can shut it off.  It’s their house.  They should be able to shut things off that they don’t want running, but there probably should be a sign warning of the consequences if they do that.

Someone once told me that the first thing many people do when they walk in the door of their home is to turn the TV on.  Maybe the ventilation system should be controlled by the same switch.  Turn on the TV.  Turn on the ventilation system.  I’m glad that wouldn’t work for everybody.

You could think about the ventilation system as a scuba tank.  When you’re under water, you wouldn’t want to shut your air off for any period of time.  When you’re in a house (a contained volume of air that is continuously being polluted by waste air from people and possessions), you’re effectively under water.  Don’t shut off your air.  Keep it simple.  Take a deep breath.  It’s okay to let it run.

Check out our website: http://www.heyokasolutions.com/

Coming soon: Average and Effective Air Change Rates: One Limburger at a Time

Sleepy From Turkey CO

November 26, 2013

I have been forced to leave more houses during energy audits because of gas ovens than for any other reason.  A gas oven burns gas.  Anything that burns can generate Carbon Monoxide or CO.  The combustion fumes move up through100_2776 an opening or chimney that generally vents just below the control panel near the burners.  If you hold your hand there, you will feel the warm, moist combustion air leaving the oven.  If the oven is old, dirty or mis-adjusted, an excessive amount of CO will get produced when the oven is being used.  The CO level is particularly high when the oven is first turned on (commonly over 1,000 ppm)  and should decrease as the system achieves a steady state operation (dropping to around 100 ppm or less).  It is advisable to keep the range hood running and venting to the outside or a window open slightly while using the oven.  CO has about the same molecular weight as oxygen so it is neutrally buoyant, but I would keep the infants out of the kitchen while the oven is warming up.

A well-adjusted gas oven flame should be blue in color, symmetrically shaped, and about ½ inch tall.  A ragged, hissing flame indicates the combustion process is getting too much air.  A yellow orange flame indicates it is getting too little air.  The flame should be continuous along the length of the burner.   If it’s not, some of the ports may be clogged, but make sure the oven is turned off and cool before making any adjustments.

I have always heard that people get sleepy from the tryptophan in the turkey, but I have begun to wonder if it’s the CO from the oven!  Enjoy Thanksgiving, but make sure your kitchen is properly ventilated!

Please visit our website: http://www.HeyokaSolutions.com

Measuring Airflow through a Return Side Tap

March 16, 2013
Image

Averaging Flow Sensor

I’m putting together an advanced on-line residential ventilation course for GreenTrainingUSA, and in the process a couple of issues came up.  One of these is testing airflow on the supply pipes to air handlers.  This popular approach includes a pipe from the outside of the building attached to the return side of the air handler.  The opening can be controlled by a damper that opens when the air handler turns on and air is drawn into the air handler along with the return air from the house.  It gets circulated around the house, blended with the other air.  Some of these systems include a control that monitors the run time of the air handler.  If the air handler does not run long enough to satisfy the ventilation requirement, the control restarts the air handler just for ventilation.  Some of these controls also monitor the outside air humidity and temperature, overriding the ventilation operation if it is too cold or too humid outside.

This approach effectively puts the house under positive pressure.  The pipe to the outside is like a hole in the return side of the HVAC system and since more air is being sent to the house than is being removed from the house by the air handler, the house is effectively under positive pressure.  The question is: How much air is being drawn through that pipe into the house?

It is often difficult to measure the flow into the system from the outside of the house either because of the location of the exterior hood or because of the irregular surface of shingles or clapboard or brick.  A measuring instrument that is sensitive to air motion is likely to be impacted by air movement on the outside of the house.

Drilling a hole in the ducting and measuring the pressure when the air handler is running, will provide the static pressure in the ducting.  Let’s say that produces – 5 Pascals of pressure.  The duct can then be disconnected from the exterior hood and a duct tester can be attached to the pipe.  Turn the air handler on again and then turn on the duct tester fan and increase the flow until there is – 5 Pascals of pressure.  At that point, the air moving through the duct test fan will be equal to the air moving through the ducting when the system is operating under normal conditions.

A simpler way to approach this is to get a small flow station and insert it into the ducting.  I recently found some remarkably inexpensive ones from Dwyer (Series PAFS-1000).  The one for 4” ducting is $7.25 and the one for 6” ducting is $8.50.  These work like simple pitot tubes.  You need to drill a 7/8” diameter hole for the sensor.  Insert the sensor into the duct and attach Channel A of your manometer to the two taps and read the pressure.  Use this process:

 

Air movement through a duct measured with a pitot tube (or averaging flow sensor):

VP = TP – SP (ΔP in Pascals)

FPM = SqRt(VP) x 253.29

CFM = A x FPM

Where:

VP = velocity pressure in Pascals

TP = total pressure in Pascals

SP = static pressure in Pascals

FPM = feet per minute

CFM = cubic feet per minute

A = area of the duct in square feet

So, for example, if you get a pressure reading of 1.3 Pascals and it is a 4” diameter duct, because you are looking at the pressure difference between the two ports, that is the velocity pressure or VP.  The FPM velocity is the square root of 1.3 times 253.29 or 329 feet per minute.  The area of the duct is 0.087 square feet, so the CFM equals 29.  This process is not perfect, but it’s a lot easier than trying to measure the flow from the outside or the duct tester approach.

We need to get better data on the performance of this ventilation approach.   29 cfm wouldn’t meet many of the ASHRAE 62.2-2010 requirements even if the air handler was running 24/7.

Visit our Website at http://www.HeyokaSolutions.com

Ventilation and Health

January 31, 2013

Sleeping StudentThere are a lot of grumblings about a requirement to add mechanical ventilation to homes.  When we gather around the campfire on a starry night, there isn’t a need for mechanical ventilation.  When we bring the campfire into the building, we a flue to take the smoke and pollutants out.  And we also bring a lot of other things into the house including the dogs and cats.  And we cook in the house and generate a lot of moisture by taking showers.  We even bring plants inside to make it feel like we were still outside.  And we tighten up the house to keep it warmer in winter and cooler in summer.  So we’re not out under the starry, starry night any longer.

Okay, but is the indoor environment really hurting us if we don’t have mechanical ventilation?  In a dry climate like Nevada, is there really enough of a humidity problem to need mechanical ventilation?  Although it is difficult to study the relationship between mechanical ventilation and health, studies do exist.  Just this morning on MSN there was an article about “20 things that are making us dumber”.  Along with “Honey Boo Boo” and excessive email that we have to check on our “SmartPhones” every 90 seconds, was “Poor Ventilation”.  The article said, “Excess carbon dioxide is doing more than wrecking our climate – it’s also making us stupid.  Researchers at Lawrence Berkeley Livermore slowly increased the amount of CO2 in a poorly ventilated room while college students attempted to solve a series of complex, strategic problems.  Not surprisingly, the more CO2 in the atmosphere, the more mistakes the test subjects made.”

In a paper in Indoor Air entitled “Ventilation rates and health: multidisciplinary review of scientific literature”, a group of very knowledgeable researchers reviewed 27 papers published in peer-reviewed scientific journals.  Their conclusion was that “there is biological plausibility for an association of health outcomes with ventilation rates”.  They also said that, “Home ventilation rates above 0.5 air changes per hour (h-1) have been associated with reduced risk of allergic manifestations among children in a Nordic climate.”

In another Indoor Air paper entitled “Association between substandard classroom ventilation rates and students’ academic achievement”, researchers from The University of Tulsa, the Illinois Institute of Technology, and the National Institute for Health and Welfare in Kuopio, Finland studied the relationship between classroom ventilation rates and academic achievement.  They determined that, “There is a linear association between classroom ventilation rates and students’ academic achievement”.

Pine Tree air freshenerSomething else to think about.  The global market for air fresheners is forecast to reach US$8.3 billion by the year 2015. Growing consumer inclination towards fragrance products such as candles for decorating their homes is poised to propel the air fresheners market.  [Global Industry Analysts, Inc.]  (Candles also put out CO.  I’m just saying.)  Air freshener advertising puts people in rooms with wrestlers and brags about how fresh it smells!  If there are no pollutants in our air, why are we spending so much money to cover them up?  In an article in the University of Washington News entitled “Toxic chemicals found in common scented laundry products, air fresheners” author Hannah Hickey says, “”Be careful if you buy products with fragrance, because you really don’t know what’s in them. I’d like to see better labeling. In the meantime, I’d recommend that instead of air fresheners people use ventilation, and with laundry products, choose fragrance-free versions.”  Her study showed, “58 different volatile organic compounds above a concentration of 300 micrograms per cubic meter, many of which were present in more than one of the six products. For instance, a plug-in air freshener contained more than 20 different volatile organic compounds. Of these, seven are regulated as toxic or hazardous under federal laws.”

I have a control on my own ventilation system that uses a sensor that was developed in Japan to react to the chemical soup emitted by cigarettes.  No one smokes in my house, but there have been numerous times when the control has activated the fan when I can’t smell anything foul in the air and I have to wonder why it is operating, but I’m glad it is.  Our homes are full of stuff that we shouldn’t be breathing.  Is it worth betting your long term health and that of your children to save the cost of a fan?

(Copies of these articles are available upon request.)

http://www.HeyokaSolutions.com

Don’t Blame the ASHRAE 62.2-2010 Standard

January 17, 2013

I have to interrupt my series on Homeowner’s Energy efficiency to say a couple of things about the ASHRAE 62.2 Standard.ASHRAE Guy

Change is always a problem.  The fact is that any change requires some rethinking and relearning.  Building science is changing all the time.  We are learning more.  We have better tools and better materials.  Buildings are getting more energy efficient and tighter.

The fact is that the ASHRAE residential ventilation standards have changed regularly.  The Standard is on a three year update schedule.  What is being referred to as the “simpler” ASHRAE 62-89 Standard is one, very small component of that standard referring to the sizing of a whole building ventilation system.  It is sort of like saying a house is simple when you only look at the insulation in the attic.  The fact is that the ASHRAE 62-89 Standard is 26 pages long.  The ASHRAE 62.2-2010 Standard is 14 pages long.

The ASHRAE 62-89 Standard is no longer supported by ASHRAE partly because of its complexity, but if you were to truly follow that procedure you have two choices in sizing the system: The Ventilation Rate Procedure or the Indoor Air Quality Procedure.
There are three steps involved in the first part of the Ventilation Rate Procedure, determining if the outdoor air is acceptable for ventilation:
1.    The contaminants in the air outside do not exceed the levels in an accompanying table and consider the size of the local community whose population is less than 20,000 and there is adequate air monitoring for three consecutive months.
2.    If the outdoor air contains any of the contaminants in the table, you can refer to another table.
3.    If you still can’t determine the quality of the air, you can perform air sampling based on NIOSH procedures.
The next part allows you to treat the ventilation air and suggests how you might accomplish that, and allows you to vary the ventilation rates during certain periods, like rush-hour traffic.
Once you have reached that point, you can refer to Table 2.3 from which you can extract the magical “0.35 air changes per hour but not less than 15 cfm per person” along with a few notes.  Also in this table are the continuous and intermittent ventilation rates for kitchens and bathrooms (which haven’t changed) along with 100 cfm per car in a garage (which is also in the IMC).

If you want to go through the second procedure – The Indoor Air Quality Procedure – you’ll need to find a copy of the 62-89 Standard.

Note there is nothing in the 62-89 Standard about calculating a Building Airflow Standard, Building Tightness Limit, Minimum Ventilation Level, etc.

The two main points of the 62.2-2010 Standard are:
1.    A whole building ventilation system to refresh the air in the house;
2.    Local exhaust ventilation to take pollutants out at the source – bathrooms and kitchens.
To calculate the whole building ventilation rate you need to know the floor area and the number of bedrooms, and you can look at the chart and figure out the CFM to meet the whole building ventilation rate.  Or if you want you can use a pretty simple formula:
0.01 x floor area + 7.5 x (number of bedrooms + 1)

Local exhaust is the same as it was in the 62-89 Standard:
Room            Continuous      Intermittent
Bathroom     20 cfm              50 cfm
Kitchen         5 ACH              100 cfm

Both Standards talk about reducing the impact on atmospherically vented combustion appliances – nothing new there.

When you buy a new combustion analyzer, it has all sorts of capabilities, but maybe all you need it for is to measure CO in the flue and you can stop there.  It comes with a detailed manual and you might even be able to take a course on how to use it to do lots of other things that are built into its sophisticated electronics.  The ASHRAE 62.2-2010 Standard can be used to simply size mechanical ventilation to cover two basic functions and you can stop there.  At the same time it has a lot of flexibility built in to fine tune the ventilation rates for a variety of applications.

If anyone can guarantee me that he or she can build me a house with the right materials and perfect indoor air quality in any location in the U.S. to surround and protect my grandchildren that will never have bad indoor air quality that will affect their health any day of the year as long as they are living there, then I will agree that you don’t need to apply any mechanical ventilation standard.  The ASHRAE 62.2-2010 Standard doesn’t guarantee perfect indoor air quality and states that clearly, but it isn’t complex to apply, and it is constantly under consistent and predictable review and welcomes input for improvement.

http://www.HeyokaSolutions.com

Imagine Yourself as an Air Molecule

September 17, 2012

There is a problem solving technique called synectics.  It refers to problem solving by analogy.  It is a technique that can be amazingly effective when trying to visualize a complex situation such as the air moving through a pipe or duct.  In my classes, I try to get the participants to imagine themselves as an air molecule being tossed around by a fan and thrown out into a duct, being pushed and shoved by the surrounding molecules, much like sports fans moving into a stadium for a game.  They have to squeeze together and slow down going through the entrance gate, and then they can move more freely in the space on the other side.  As they move through ramps and hallways toward their seats, they have to slow down moving around corners.  Moving from a narrower hallway to a wider one, all the congestion seems to almost disappear.

People as Air Molecules

Air moves through ducting the same way, but how much resistance do components like elbows and vent caps create?  If we want to get the air to move through the duct at a predictable rate, we need to know stuff like that.  Grille manufacturers are good at providing useful information, providing static pressure and throw at different velocities.  But I don’t know if any vent cap or hood manufacturer that provides that sort of information.  There are some interesting tables (one of which is available in my book Residential Ventilation Handbook) in places like the HRAI training program.  I decided I needed to verify that information.  I needed to do some testing on some hoods.  (I have listed those results on our site with each of the hoods/caps that we sell.)

There are three components to designing a duct run: the actual length of the ducting, the equivalent length of the fittings, and the effective length of the system.  The actual length is the measured distance from beginning to end.  The equivalent length is an approximation of the resistance of each fitting in terms of duct length. And the effective length is the sum of the actual length and the equivalent length.  It is the distance that the air feels as it moves through the system.  So if you are standing there in the attic looking at where the bath fan is installed and where you want it to leave the building, it may not look all that far.  But when you start adding up all the fittings and stuff, 20 feet of actual length approaches 100 feet of effective length in a hurry.

And looking at a table like this one, it’s no wonder that it takes so long for clothes to dry in a clothes dryer.  If you’re trying to push 200 cfm through a 4” diameter duct, the air is looking at 2.5 iwg or 625 Pascals for an effective 100 foot run!  Longer drying times mean more energy consumption and greater impact on the fabrics.

Airflow (cfm)

Duct diameter

Pressure in 100 feet duct  iwg/Pa

50

3”

0.8/200

4”

0.2/50

6”

0.025/6.25

100

3”

3.0/750

4”

0.7/175

6”

0.09/22.5

200

3”

>10.0/>2500

4”

2.5/625

6”

0.3/75

Bath fans are certified at 0.1 iwg so it is little wonder that they are not running at the rated flows once they are installed.  But check out what happens to the resistance when you increase the size of the ducting.  A hundred cfm moving through 100 feet of 4” duct experiences 175 Pascals of pressure.  Increasing the ducting to a 6” diameter drops the pressure to 22.5 Pascals!  So if an existing bath fan is tolerably quiet in a home that needs to meet ASHRAE 62.2, it may get there by increasing the duct diameter and improving the path to the outside.  (Note that the sound produced by the fan will decrease as the resistance decreases.)

It is important to realize that these numbers are for rigid, smooth ducting and not flex duct.  Flex ducting is 33 times rougher than galvanized pipe and 100 times rougher than PVC piping.  Fan manufacturers have gotten pretty good at addressing these performance problems and some of the new fans with the EC motors automatically adjust their performance to meet the resistance of the ducting.  (I wish crowds at sporting events would do that!)  But the sound level of even these sophisticated products will increase as the resistance increases, so it is still a good idea to make the duct run as short, straight, and smooth as possible.

Make it easy for the air to get through the ducting all the way to the outside and you’ll have better airflow.  Just think of yourself as an unhappy air molecule the next time you are stuck in traffic with all the other air molecules trying to get to the same place at the same time.

Basement Dehumidifiers

September 11, 2012

Basement Dehumidifier

Dehumidifiers use a lot of power, in the range of 600 to 850 watts.  If it’s running 24/day, 365 days a year that’s 5,256 to 7,446 kWh per year or about $950 to $1,200 per year at eighteen cents per kWh.  That’s like $100 per month!  But wait, you say, they don’t run 24/365.  They do if the homeowner has cranked the control all the way to Continuous or doesn’t know how to set it.  I have been in people’s homes where I have saved them about half their electricity bill by simply turning down the dehumidifier.

I put a data logger down in my basement this summer when it was really hot, humid nasty outside, running with an outdoor dew point above 70 F.  The temperature in the basement averaged about 70 F and relative humidity averaged about 70% RH.  The dew point cruised at about 61 F.  My data logger was recording the air temperature, humidity and dew point.  That doesn’t mean that there weren’t surfaces in the basement that weren’t below 61 F.  Most of the mass of the basement has been there long enough to reach an even temperature, however.  So there may be dark, damp corners, but for the most part, the entire basement and all the stuff in the basement was above the dew point.

Many of the new IR cameras have a dew point screen that can be used to figure this out.  Or you could put in a data logger or hygrometer and figure it out.  There are so many dehumidifiers running in so many places that we could make a major impact on energy consumption just be getting them set up and working properly.  (There is a nice little dew point calculator at: http://www.decatur.de/javascript/dew/index.html .)  There are a bunch of places that sell hygrometers that will provide the temperature and humidity.  You can plug those numbers into this calculator and get the dew point.

The dehumidistat controls have vague settings from OFF to NORMAL to

Dehumidifier Control Panel

DRYEST to CONTINUOUS.  What does NORMAL mean?  There is a difference in using the dehumidifier to maintain a comfortable humidity in the living space and the right humidity to keep mold from growing in the basement.  For the basement application, the dehumidifier should be set to the lowest possible setting to meet the need.  It should be set so that the RH is below the dew point.  It should definitely be cycling on and off.

Many of the product performance numbers are based on operation at 80 F and 60% RH which is a pretty high temperature for a typical basement (or even a house).  Some of the manufacturers rate their dehumidifiers at 100% RH which is not a condition you would ever want to see in a basement!  One measure of the efficiency of these machines is how many pints (Energy Star rates them in Liters) it can remove per kWh.  If you take the stated Water Removal Capacity (in pints) and divide it by 24, divide that by power consumption in watts and multiply the whole thing by 1000, you’ll get the pints per kWh.  In the handful of units that I looked at they ran from a low of 3.47 (1.8 L/kWh) to 6.49 (3.07 L/kWh).  There is an interesting little closet sized unit that came in at 10.65 (5.04 L/kWh)!  Something seems a bit off with that one.

Why is the dehumidifier in the basement?  If it is to keep the mildew off the suitcases stored in there, it just has to keep the RH low enough to prevent condensation.  If it is to remove standing moisture in the basement, then you probably need a pump instead of a dehumidifier!  If the house having an energy audit has a dehumidifier, it should be included in the audit.  It is more of an energy load than a whole lot of light bulbs.