Tag Archives: indoor air quality (IAQ)

Lessons learned: 1st floor ventilation

We have a special friend. His name is Erv, and he brings us fresh air into the house year round. Other people have the same friend, but they call him ERV, or sometimes by his full name: Energy Recovery Ventilator.

The ERV is a well appreciated equipment. Because our house is almost completely airtight, we need mechanical ventilation to remove the stale air and bring in fresh air. The ERV does just that, assures good indoor air quality, and in the process keeps us comfortable with the enthalpy wheel. It acts as a heat exchanger and removes excess moisture.

I like to put it this way: Using the ERV is like keeping windows open during the winter to get fresh air in, with the exception that it doesn’t get cold. It works so efficiently that it helps us to delay our heating season by up to four weeks.

The fresh air is distributed across our 1st floor apartment through a system of ducts, supplies and returns. I was about to embark on the ductwork installation project for the 2nd floor. But before doing so, I wanted to review our 1st floor ventilation system: What worked, and more importantly, what could we have done better?

Stale rooms (with a lowercase s)

The 1st floor ventilation system has fresh air supplies in key rooms to assure fresh air distribution across the apartment. A series of undercut doors, ‘indoor pressure balancers’ and ‘between room vents’ help move air from room to room and to eventually to the returns in the two bathrooms.

We can easily flush stale air out of the apartment by cranking up the ERV. However, if we run the ERV on the low setting (low airflow), the library and living room remain somewhat stale for longer than any other rooms in the unit.

In other words, the fresh supply air is not mixing sufficiently with the room air. The velocity from the fresh air supply in the foyer is good, but too slow when moving on to the library and living room.

To avoid something similar on the 2nd floor, I plan on adding a fresh air supply to the library and living room.

Noise transmission

The first time we fired up our first floor ventilation system, it sounded like a roaring jet engine. That problem was quickly solved with two three-foot pieces of insulated flex duct connecting the ERV to the rigid ducts. I made sure we had a 90 degree bend in each flex duct, and our ventilation system fell completely silent – almost.

While the noise transmission from the ERV is under control, we still had some transmission from room to room. For example, the fresh air supply of the office and foyer are connected by a six foot duct. The noise transmission through this short duct is as such that two people – one in the office and the other in the foyer – could have a conversation with each other. The longer the duct between supplies, the more faint the noise transmission.

To minimize the room-to-room transmission on the 2nd floor, I plan on using a three foot piece of insulated flex duct with a 90 degree bend right after every supply to act as a sound muffler. This will also increase friction and reduce velocity, but I will try to make up for it through more generous duct sizing.

2nd floor ventilation layout

The plan below shows the 2nd floor ventilation layout with the improvements mentioned above:

  • Using flex duct at each supply as a sound muffler to reduce room-to-room sound transmission
  • Adding fresh air supplies to the library and living room to improve mixing with the room air and a more efficient flushing of the stale air, even at lower airflow rates.

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Onset of nerdiness

Strange things happen once one embarks onto the deep energy retrofit road. For instance, a level of nerdiness sets in.

You don’t just turn on the thermostat in fall. You make a note about when exactly you turned it on. This year, it was the evening of November 1st.

Not nerdy enough? How about this:

Back in the day, when I was more than young – when I was a kid – a hybrid of joy and eager anticipation clocked in once a week, triggered by the release of the next episode of a science comic book.

Some may argue that things haven’t really changed that much, except that the comic book was replaced by the monthly arrival of our utility bills. I devour them almost immediately, and they almost always make for some interesting reading.

Such as our natural gas bill for last month, which claims that we used more gas in October 2013 than October 2014!

gas-bill-01

Therms 10/2013: 32.51
Therms 10/2014: 22.52

Average daily therms used 10/2013: 1.02
Average daily therms used 10/2014: 0.75

That seemed strange, particularly because this October seemed so unseasonably cold.

Well, let’s separate fact from fiction. October 2013 was cooler, at an average daily temperature of 50 degree Fahrenheit, compared to 51 degree Fahrenheit for October 2014.

That still doesn’t explain away the difference in natural gas consumption. Nor do the extra two days on the October 2013 bill, although they could account for as much as 2.04 therms. To get to the bottom of this, I have to turn to the Energy Recovery Ventilator (ERV).

With an almost airtight house like ours, mechanical ventilation is less a choice than a necessity. It maintains good indoor air quality (IAQ) by removing pollutants and excess moisture, and as such protects us from what is known as the sick building syndrome.

The ERV doesn’t just ventilate the building, but it also has a built-in heat exchanger, the enthalpy wheel. This makes it an extremely useful piece of equipment, particularly during the heating season, as we get a supply of fresh air without the typical heat loss.

We had our fair share of ERV problems last year, starting in October. The air in the building got stale rather quickly, with no functioning mechanical ventilation. To maintain good indoor air quality, we fell back on the age old method of non-mechanical ventilation – opening the windows.

The problem for us was that there is no heat exchanger when you open the windows. We got plenty of fresh air – but is was cool October air. With that we had a lot of heat loss, which led us to turn the heat on about a month earlier than usual.

And that, ladies and gentlemen, probably explains the difference of 10 therms in the gas bill between this and last year.

If you find this remotely interesting, you have officially joined the club of nerds!

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Picking an ERV

Design workshop

ERV – keeping the heat!

ERV performance test

ERV croaked – Part 1

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Lacquering what I like

The paint has come off, and now needs to get back on. Although it won’t be paint – it will be clear, VOC free lacquer.

Having gone through a couple of tubes of wood putty and many sheets of sandpaper, I was ready to dust off the vertical trim and start lacquering.

Two coats, with a drying time of six to eight hours between each coat. The lacquer brings out the beautiful warm white oak color and adds a nice sheen to the trim.

I stay mindful about our health and safety as well as the immediate and long term indoor air quality (IAQ) and kept using the VOC free Acrylacq by SafeCoat. No solvents, no nasty fumes or smells. Why would I ever want to use the conventional, VOC based paint products?

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Range hood recap

What is there to a range hood? Well, it depends on how deep you want to dig.

In simple terms: You want a functioning range hood over your stove to dump cooking odors and moisture to the outside. It helps a long way with maintaining good indoor air quality (IAQ). Who really enjoys smelling the cooking from a few days ago across the house or wiping the cooking grease film off of the living room furniture?

But simple is boring! The nuances that surround the range hood are much more interesting.

Nuance heaven

I mentioned it, and I’ll say it again: Be picky about the ventilation rate!

Logic suggests that a hood with a high ventilation capacity would be more effective in exhausting cooking odors. But it wouldn’t necessarily be efficient. How much airflow would it really take? Any additional flow beyond that represents wasted electricity.

Widely referenced residential ventilation rates can be found in the ASHREA Standard 62.2. The minimum required exhaust rate for user operated range hoods is listed at 100 cubic feet per minute (cfm). The standard was published back in 2003. I expect that it will be updated considering the increasing emphasis on reducing air leakage in buildings.

Our freshly installed hood has two ventilation settings – 100 cfm on low and 250 cfm on high. There should be a balance between the amount of air exhausted to the outside and the makeup air.

High capacity range hoods (starting at 600 cfm) may throw that balance off and begin to depressurize the building, which can cause a number of problems.

Take open combustion appliances, such as a water heater for instance. With the high capacity range hood cranking at full speed, the exhaust fumes from the water heater may backdraft into the building.

Or – during the summer months – a high capacity range hood may be the culprit for hot and moisture laden air leaking into the building. If the building is air conditioned, interstitial condensation forms on the cooler interior surfaces, which can lead to mold problems.

Options, options, options…

Have you seen those range hoods that ventilate back into the building? They are the preferred option in some particularly airtight Passiv Haus buildings. A charcoal filter in the hood should eliminating the cooking odors – as long as it is regularly replaced.

Suppose we are on top of the filter maintenance. We still haven’t addressed the additional moisture load from the cooking.

Let’s ventilate to the outside instead and think about managing the makeup air. Opening the kitchen window a crack while the range hood is operating would be an option. Other folks borrow from commercial kitchen design, and install a fresh air supply duct that terminates near the stove.

Either option carries an energy penalty: Introducing unconditioned air into the conditioned building interior. This may be less of a problem in the winter when heat generated from the cooking may somewhat lessen the energy loss. During summer, however, the make up air would be hot and humid and one can start to count the energy penalty in sweat beads.

Why hasn’t anyone come up with a heat exchanger for range hoods, similar to the Heat or  Energy Recovery Ventilators (HRV’s or ERV’s)? The engineering challenge lies in the cooking grease.

Read ERV or HRV installation manuals, and you are instructed not to install an exhaust in the kitchen. The cooking grease will ruin the heat exchanger, or at a minimum shorten its lifespan.

Should we grease up some sharp minds and try to solve this fat engineering challenge? Even if we do, the grease removal or management would likely require additional energy input. That flies in the face of the energy reduction goal.

Going back in history to a time where energy or electricity was precious can be enlightening. Jeremy Spates, who studies historic preservation at the School of the Art Institute of Chicago, pointed out that “especially in Chicago, cooking was probably done with coal or wood in an iron stove, but with a smaller blaze than one might use in winter”.

Larger houses had the kitchens in the back or the basement, such as the Clark House. I only can speculate to what extent this may have reduced the heat gain from summer cooking.

Jeremy also pointed out that outside the urban environment, some houses (or mansions) in the eighteenth and nineteenth centuries had outdoor kitchens where the summer cooking took place, thus keeping the extra heat out of the main building.

Now here is a good idea – simple yet effective, and may be more suitable for energy efficient buildings than we realize.

The concept

Kitchens are difficult to manage in airtight homes. Why shouldn’t we place the kitchen outside the airtight envelope – at least on a seasonal basis. It would address the excessive heat gain, moisture load and makeup air issue. It would solve a big headache.

This idea has been lingering for a while and our back porch has come up as a potential space where we could conduct our summer cooking. The deeper we get into the summer, the more I warm up to the idea and I am increasingly glad that we extended the gas line into the back porch – just in case we decide one day that summer cooking on the porch is the cool thing to do.

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Chasing after a star – Energy Star for a range hood

When preparing a blog post, I often ask myself: “What would be a one sentence summary”? For this post, I can boil it down to one word: Tenacity!

During my indoor air quality (IAQ) research, I learned about the importance of picking the right range hood:

  • The range hood is critical for moisture management and IAQ.
  • One has to be careful not to over-ventilate in tight homes – i.e. depressurize the building.
  • A ventilation capacity of 150 cfm is recommended for tight homes.
  • Stay away from powerful downdraft range hoods (600 to 1200 cfm).
  • Exhaust the range hood, and with it the moisture from cooking, to the outside.
  • Use an energy efficient, preferably Energy Star certified product.

See also:

It is that last item that required my tenacity – procuring an Energy Star certified product.

By looking at the various products, it is easy to conclude that a sleek design is what sells a range hood. Efficiency is really not much of a focus or selling point.

The Energy Star product list provides a refreshing departure from the sleek status quo. Here one can indulge in rows of energy efficient models. Although, after the first enthusiasm passed, the typical energy rating of 3.8 cfm/watt seemed disappointing.

Imagine my surprise back in 2011 when I read 8.6 cfm/watt. A Whirlpool range hood had appeared on the Energy Star list, and it promised to move air with a lot less electricity.

Fast forward a few months. The promising model disappeared from the Energy Star product list. I thought it would be wise to double check the product’s energy efficiency rating and searched the web – no luck. Was this one of those “too good to be true” cases?

When I called Whirlpool, no one seemed to be able to get their hands on the range hood’s energy efficiency rating either. One customer service agent finally revealed that the model had been discontinued. Oh my!

Back to 3.8 cfm/watt? I was left scratching my head.

Coming up with energy efficient range hoods can’t be rocket science! Great advances have been made in the development of extremely efficient ventilation motors. Just look at some of the current ERV and HRV products. Why do these advances not translate into the field of range hoods?

I kept checking the Energy Star product list every other month – and bingo! AirKing has a new model (Essence EB series) listed with 5.4 – 6.7 cfm/watt at an airflow of 107 – 132cfm. That is quite an improvement over the ESDQ AirKing model we used in the garden unit (3.8 – 4.0 cfm/watt at an airflow of 159 – 163 cfm).

Let’s buy it! But where? It was nowhere to be found … not among the online retailers, or even on AirKing’s web page.

It was time to pick up the phone. A call to AirKing in November, 2012 revealed that the new model was scheduled to hit the market in February 2013.

But why was it on the Energy Star product list months prior to that? AirKing submitted a prototype to Energy Star for testing and certification. Once certified, it made it onto the Energy Star product list. But AirKing still had to get ready for production.

This doesn’t make it easy for the consumer; it’s confusing and requires tenacity. I could afford to spend the time on tracking the products and wait this out. But what about other buyers?

I finally placed my order for range hood AirKing Essence EB at the end of April 2013, with a lead time of 10 days. Manufacturing was still ratcheting up.

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