Posts Tagged ‘Energy Star’

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.

Homeowner’s Energy Workbook Part 10 Component U Values

January 22, 2013

Now that we have the total U value for the house, we can start looking more carefully at individual component U Values.  P1000274Considering the single story house we just analyzed, it is about 1,000 square feet.  It has a nice, flat 1,000 square foot attic floor insulated with fiberglass batts that have an R-value of 19.  There is also sheetrock covering the ceiling that also has a small R value, and there are the ceiling joists that hold the structure together.  Would it be worthwhile for the homeowner to have a contractor come in and blow in another 24” of cellulose insulation?  How much would it save?

To keep things simple, let’s say that R19 is the average R value[1] of the whole ceiling.  The U value = 1/R, so the U value is 0.053.  To get the U value of the whole ceiling element, multiply the U value times the area: 0.053 x 1000 or 52.6 UA.

We have to multiply the UA value times the Heating Degree Days (4151 in this case) times 24 hours in a day, we get 5,243,368 BTUs for the year or 52.43 Therms (because there are 100,000 BTUs in a therm). And since a therm costs $1.47 it costs $77 per year for the heat going through the attic floor or just about 32% of the cost of heating the whole house.

What would happen if we had someone blow in 24” of cellulose insulation into the attic?  The R-value of loose fill cellulose is about 3.7 per inch, so that would be about R-89 plus the existing R-19.  So we would have R-108 in the attic.  That would reduce the heat loss (going through the same calculations as we just did for R-19) to 9.25 therms or $13.56 for the year!  The insulation itself would cost about $900.

What about a window?  Let’s say we have a single pane wooden window without a storm window.  Would it be worth it to replace it?  Two issues to think about here.  One is the conductive loss through the window and the second is the convective loss, the drafts around the edges and between the sashes.  Before we had special tools like blower doors to use to test for air leaks, we used to estimate the leakage of the windows by inserting a quarter in the gaps!  The problem is that we can’t really get a good average number for the convective savings, but we can determine the conductive savings.

Let’s say it’s a thirty-two inch wide by forty-five inch high window or ten square feet.  If it has a single pane, its U value would be 0.90 or a UA of 9 (10 x 0.9).  That would mean that window would require 8.9 therms or $13.18 to heat for the year.

If we replaced it with a new double paned window with a 0.30 U value, it would cost just a third of that or $3.95 in heat for the year.  We would have to replace about seven windows to get the same savings as we would in adding some insulation to the attic.

We are neglecting the convective savings from the windows, however.  But the process works for estimating savings for any energy improvement.  Before adding insulation to the attic, it is very important to seal all the holes and cracks and gaps where wires and pipes and chimneys come through.  It is important to mark where electrical connections are that will need to be serviced in the future.  It is important to carefully seal the tops of the exterior walls.

Now you know, however, that if someone tells you they can sell you a window that will double the U value of the windows you have, that that would be a bad deal indeed!

Next Time: Fuels and their Ratings

[1] To calculate the average R value, one needs to determine the R value in the space between the ceiling joists, the R value through the joists themselves, and calculate how much of the ceiling is the space and how much area are the joists.  This is a really worthwhile calculation when one looks at things like attic hatches where the R value can be really poor and have a major impact on the overall average R value of the whole ceiling, but we’re going to keep it simple here.

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: .)  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.

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 < 75%

SRE ≥ 75%




1.2 (0.57)

0.8 (0.38)


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.