Tag Archives: ERV

Chiberia 2019 – ERV hibernation

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Two aspects of our mechanical system fell victim to the Siberian express that ran over us during the last week of January. One of them was the Energy Recovery Ventilator (ERV).

The ERV typically operates down to 10 degrees Fahrenheit (-12 degrees Celsius). Below that, the enthalpy wheel freezes up, and a temperature sensor in the ERV shuts the unit off. That meant that we were without mechanical ventilation for three days.

That’s not too much of a problem, as we could crack open a window or two to get fresh air into the building. The down side was the big energy penalty when opening the windows.

I can report that it didn’t get stuffy despite the presence of two human beings and two dogs, and that humidity levels stayed under control as was evident by the minimal condensation at the bottom of the windows during the early morning hours.

Our ERV is an earlier model of the RecoupAerator 200DX. With the current model, temperatures below 10 degrees Fahrenheit (-12 degrees Celsius) should not be an issue as the unit comes with a pre-heating element.

The element is built into the fresh air intake and is tied to a temperature sensor which pulses it on and off as needed to maintain the incoming air at 12 degrees Fahrenheit (-11 degrees Celsius) to prevent the enthalpy wheel from freeze up. This allows the unit to operate at outdoor temperatures below 10 degrees Fahrenheit (-12 degrees Celsius). And if combined with a solar PV array, it can even operate at a low carbon footprint.

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Wet duct insulation!

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Let’s stick with the ventilation subject for a moment, dear readers, because I need help with a hack. I hope that some of you can point me in the right direction. Here is the problem that needs solving:

The duct insulation in the flex ducts that connect to my ERV is getting wet every winter.

Why do I have the flex duct in the first place?

The purpose of the flex duct is to stop vibration transmission from the ERV to the rigid ducts.

Why does the duct get wet?

During the winter month the fresh air intake carries cold air and the exhaust duct from the ERV to the building exterior does the same. This cold air often cools down the duct below the dewpoint. That causes any moisture that is lingering in the flex duct or that gets past the duct sleeve to condense on the flex duct core. It is subsequently absorbed by the fiberglass insulation around the flex duct. Theoretically, this should not happen. The outer duct sleeve should prevent any air, and with it moisture, from getting to the flex duct core.

The weak points in this system are where the flex duct connects to the rigid duct, and even more so, were it connects to the ERV.

I use sturdy duct zip ties and even have the tool to zip them as tight as possible. But even with utmost diligence, it appears impossible to make these connections airtight.

An added complication is that the ERV needs occasional maintenance, which in some cases requires me to disconnect the flex ducts from the ERV. The zip tie system makes disconnecting and reconnecting fairly easy, but apparently fails to get it 100% airtight. I am also concerned that handling the duct during the maintenance operations may lead to breaches in the duct sleeve.

Solutions?

Is there a product out there that would be better than flex duct but still provide the vibration isolation? Or is there a better system for connecting and sealing the flex duct to the ERV?

Whatever a better and air tight solution may be, it must allow for easy disconnection and reconnection of the duct to the ERV.

Any suggestions? Who’s going first?

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Ventilation closet framing

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My recent activity has been driven by my intent to get to the electrical installation. The last framing item that was standing in the way was the ventilation closet, because of its access doors and the issue of sound management.

To understand the decision making process, let’s look back at the 1st floor ventilation closet, which is directly underneath the 2nd floor closet and about the same size. But the access doors to the closet are on the bedroom side.

Our rationale was that in addition to accommodating the ERV, the ventilation closet would have additional shelf space for clothing and linens. The one drawback was the noise issue when the ERV was running. And it should run during the night hours when you are sleeping, at least during the heating season.

Don’t get me wrong, the ERV doesn’t make a lot of noise. It actually runs very quietly. And most folks would probably think of it as white noise. Nevertheless, the noise could be eliminated – or more accurately – shifted from bedroom to the living room. Because no one would be sleeping in the living room, the little noise the ERV would make wouldn’t bother anyone.

With that lesson learned, I was posed to place the access door to the 2nd floor ventilation closet on the living room side. And once I had scored two very nice salvaged oak doors from the ReUse Depot, I was finally ready to finish up the framing.

I will write more about additional sound management efforts for the ventilation closet in upcoming posts. Stay tuned!

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2nd floor ventilation system

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I had a plan for the 2nd floor duct installation, and I had my six and eight inch round ducts. But they are not your everyday ducts. They are special for a couple of reasons.

Quality material

First off, they are called GreenSeam or GreenSeam Plus and they have built-in neoprene gaskets in the longitudinal seams. Once you snap and lock the pipe together along the longitudinal seam, the gasket should render it airtight.

 

The GreenSeam Plus, which is easily identified by the green band around the pipe end, has a gasket that is supposed to seal the travers joint, in addition to the longitudinal gasket. Furthermore, the GreenSeam ducts come in 26 gauge, compared to the thinner 30 gauge ducts you typically find in the big box home improvement stores.

In summary, I have sturdy 26 gauge ducts with gaskets for air sealing at the traverse and longitudinal joints. And the last time I checked, they were only incrementally more expensive than the big box products.

Air tightness

The ventilation system duct work should be airtight for a number of reasons. You want to control where the fresh air is delivered and where stale air is removed from the building. Leaky duct work would deliver or remove air where it is not needed, or where it could even be damaging.

The GreenSeam duct products with their gaskets make it a whole lot easier to air seal your ventilation system. To nip any remaining leaks in the bud, I sealed all seams on the outside with duct mastic. This is particularly important on elbows and tees, which have moving parts and joints without gaskets. And, of course, I sealed around all sheet metal screws I used to hold the duct work together.

 

The duct mastic also helped with air sealing the transition from a rigid to a flexible duct. The flexible duct was pushed over the rigid duct after it received a good coating of mastic on the duct end. Everything was then tightened up with a big zip tie.

Installation

Now that we had the technical aspects and quality control issues addressed, it was time to throw some ducts around!

The installation started at the ERV end for the supply and return lines. From here I could run the ducts to the various supply and return points (see also 2nd floor ventilation layout in preceding post).

We ran all the ducts in the attic above the 2nd floor ceiling joists. We had to lower a couple of ceilings toward the back end of the building (the bathroom and second bedroom) to have sufficient space for the ducts. The attic toward the front was tall enough to fit everything in.

A big thank you to our friends Vincent and Rubani for assisting me with the installation!

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Lessons learned: 1st floor ventilation

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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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