Posts Tagged ‘ventilation’

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

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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

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

HRV/ERVs and Energy Star

August 27, 2012

HRV with cover removed

I was asked recently about HRV/ERVs and Energy Star.

  1. Energy Star V3 does not require the use of HRVs or ERVs, but it does require that the ventilation system must be designed and installed to meet ASHRAE 62.2-2010.
  2.  There is no Energy Star program for HRVs or ERVs in the U.S.
  3. There is an Energy Star program for HRVs and ERVs in Canada that was developed specifically for Canada.  This program has operated for approximately 2 years using tier 1 specifications.  Tier 2 specifications went into effect in July of this year.  Note that these are Canadian Tier designations.
  4. US EPA did not replicate the Canadian Energy Star program because it was not clear that the Canadian specifications were in the best interests of U.S. homeowners.  The main issue being that there is no energy savings value for the -25°C (-13°F) requirement.  It is a too infrequent and geographically isolated condition in the continental U.S.
  5. Canadian specifications do not take into account the AC season which is an imperative consideration in Iowa and virtually all the U.S.

I would recommend the following requirements for HRV/ERVs in the U.S.:

  1. Products must be HVI certified;

    Attic HRV installation

    Attic installations can make servicing difficult.

  2. Product must be installed in an obvious location where it will be easily serviceable;
  3. Select and compare units at the airflow specified for the project.  (For any product the higher the airflow the lower the efficiency, the lower the airflow the higher the efficiency.);
  4. The net supply airflows (in cfm) used during testing at these two different temperatures must be within 10% of each other, and specified in product literature and labeling;
  5. If the home is located in a cooling dominated climate, it is advisable to evaluate the Total Recovery Efficiency (TRE) of the product as well as the Sensible Recovery Efficiency (SRE), looking for TREs in excess of 40%.

Supply Temperature

Min. Fan Efficacy at supply tempCFM/Watt (L/s/W)

SRE

°C

°F

SRE < 75%

SRE ≥ 75%

Heating

0

32

1.2 (0.57)

0.8 (0.38)

65%

The following are definitions from Section III of  HVI-Certified  Heat Recovery Ventilators and Energy Recovery Ventilators (HRV/ERV)

Sensible Recovery Efficiency (SRE):  The net sensible energy recovered by the supply airstream as adjusted by electric consumption, case heat loss or heat gain, air leakage, airflow mass imbalance between the two airstreams and the energy used for defrost (when running the Very Low Temperature Test), as a percent of the potential sensible energy that could be recovered plus the exhaust fan energy.  This value is used to predict and compare Heating Season Performance of the HRV/ERV unit.

 

Total Recovery Efficiency (TRE): The net total energy (sensible plus latent, also called enthalpy) recovered by the supply airstream adjusted by electric consumption, case heat loss or heat gain, air leakage and airflow mass imbalance between the two airstreams,  as a percent of the potential total energy that could be recovered plus the exhaust fan energy. This value is used to predict and compare Cooling Season Performance for the HRV/ERV unit.

Unbalanced HRV/ERVs

August 23, 2012

Image

I have been disturbed to find that many HRV/ERVs are installed without any concern about balancing the system.  (Click on HRV Survey for a CMHC study of system installations.)  When I first got started with these things, it was a mandatory step in the process.  They also had to be ducted independently from the HVAC system ductwork.  That is seemingly a rare installation these days.  But if you think about it, in the extreme situation when there is no airflow coming into an HRV/ERV from the outside, the system is working as an exhaust fan.  There is no heat or enthalpy recovery.  In the opposite extreme, when there is no airflow coming into an HRV/ERV from the house, the system is working as a supply fan and there is zero heat or enthalpy recovery.

The efficiency numbers that are provided through Home Ventilating Institute (HVI) testing are at the balanced condition – same amount of airflow in each direction.  If the efficiency of the heat or enthalpy recovery matters, then it should be operated in a balanced condition.  The vast majority of these units have internal fans.  If the HRV/ERV output to the house is connected to the return side of the air handler, when the air handler turns on, it will depressurize the return duct and suck the air from the HRV/ERV increasing the supply flow through the unit.  It turns out that this unbalanced condition has more impact on the house than it does on the efficiency of the HRV or ERV.  If the house is in a heating dominated climate, it may not be advisable to operate it in a higher supply volume configuration because it may force humidity in the house into the building system components.

It is certainly more expensive to provide independent ductwork for HRV/ERVs.  It takes extra work to actually design the ductwork and calculate the resistance.  It takes extra work to measure the flows and balance the system.  It takes extra work to commission the system.  But if houses, especially tight houses, are going to depend on their mechanical ventilation system for good indoor air quality, these are steps that should be taken.

Duct Design and Static Pressure

As the static pressure of the system increases, the fan/blower has to work harder, and the airflow decreases.  For example, blowing 100 cfm through 100 feet of 4” diameter duct has a static pressure of Image0.7 iwg or 175 Pascals.  Increasing the duct diameter to 6” drops the pressure to 0.082 or 20.5 Pascals.  The Effective Length of the ducting is the sum of the Actual Length and the Equivalent Length of the fittings like the elbows and grilles and exterior hoods.

The exchanger unit itself has a high static pressure because of the resistance of the core and the filters.  But that is the pressure that it was designed for and tested at.  If that resistance is much higher than the resistance of the duct work, then the resistance of the duct work won’t make much difference in the performance of the system.  In the case of simple bath fans, for example, if the duct run is so bad getting to the hood, it really doesn’t have a great deal of impact on the flow if it is a restrictive hood!   The damage, as they say, has already been done.

For a “back-of-the-envelope” calculation you can figure that a 90 degree elbow has an equivalent length of 10 feet, a wye fitting with equal takeoffs is also about 10 feet, a tee fitting is about 50 feet, a tapered increaser about 4 feet, a typical exterior supply hood with no back draft damper about 35 feet, and an exhaust hood with a damper about 60 feet.  So if you have an installation with 30 feet of actual length, 4 elbows, and an exterior exhaust hood, you would have an effective length of 130 feet or approximately 0.11 iwg for 6” duct work.  If you have about the same run on the intake side, the hood is less restrictive, so the run is very close to 100 feet.  And then you have the connections to the rooms.  Here is a quick duct calculator from Hart & Cooley, the grille manufacturers: Duct Calculator.  (There is more information on this in my book Residential Ventilation Handbook.)

The effective length can add up quickly, so the installation needs to be thought through for performance not just for convenience.  Since the system needs to be maintained – filter and core cleaning, at least – the exchanger should be located someplace very accessible and not buried in an attic or crawl space.  If you’re going to pay this kind of money for a ventilation system, you want it to work right.  You want it to work as expected.