Posts Tagged ‘mechanical 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

What is my house doing to me?

November 22, 2016

Fall River, MA

hhe-kitchen-hazards“Why do I wake up in the morning with a headache?”  “Why is the house so dry in the winter?”  “What are VOCs?”  “Does my house have a radon problem?”  Can you answer all these questions?  When we do an energy audit on a home, we are looking for issues that impact the heating and cooling loads.  But the same tools that we use for thermal analysis can be used to highlight unhealthy or hazardous conditions in a house.  The BPI Healthy Home Evaluator (HHE) certification merges energy efficiency and home health together.

On Tuesday the 15th and Wednesday the 16th of November, a first in the nation BPI HHE class was held at Bristol Community College.  The BPI credential was developed in partnership with the Green & Healthy Homes Initiative.  “It builds upon the BPI Building Analyst (BA), Energy Auditor (EA), and/orbpi-logo-4c Quality Control Inspector (QCI) certifications to verify competencies required to conduct in-depth healthy home environmental risk assessments.  The Healthy Home Evaluator assesses home-based environmental health and safety hazards and provides a prioritized list of recommendations to address those hazards.”

The two day class extensively reviewed numerous aspects of HHE skills including the liability issues involved in stepping into a hazards and health analysis, resident interviews, the identification and interpretation of hazards, and the seven “Keep Its” developed to clarify the primary elements of the program:

Keep it:

  1. Dry
  2. Clean
  3. Safe
  4. Ventilated
  5. Pest-free
  6. Contaminant-free
  7. Maintained

The class was able to apply these techniques to the test cabin located in the BCC weatherization laboratory while going through a typical field analysis incgas-leaksluding gas leak detection, CO monitoring, combustion safety testing, blower door testing, and ventilation system verification.  Added to these was asbestos pipe insulation, messy counters including cigarettes and spilled coffee, long blind cords, children’s toys in the oven, toxic chemicals in a cabinet, and a hazardous carpet.  These hazards were so common and obvious that the students missed many of them despite the fact that they had been sensitized to seeking them out.  Like odor fatigue, elements such as these are so common in an energy audit that they are simply overlooked.

What are the Lower Explosive Limits for natural gas, propane, and gasoline?  What is the impact on house pressures of a blocked return air vent?  Is it a water stain on the ceiling or sign of a mouse nest in the attic?  There are dozens of questions about a house.  Some of them are no problem at all.  Some of them are chronic, long term problems, and some of the are acute problems (like CO) that should be addressed immediately.

This is an evaluation credential.  There is so much to know about this stuff that it will take years of testing and experience to know the ins and outs.  But if we can get homes safer and healthier it will save a great deal on medical care which should appeal to health insurance companies and all of us.

If you wanbristol-community-college-1t to learn more about this stuff, Bristol Community College will be conducting more of these classes at 1082 Davol Street, Fall River, MA 02720 – 774-357-3644

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