Tag Archives: research

Fanning over efficiency

There are several useful tools in the cyberworld that can assist with making energy efficient decisions. One of those tools is the Energy Star website with its Product Finder section.

But there is also a cautionary tale here – hidden in the fine print, if you will. I recently ran into this head on, while looking into ceiling fans.

One of the big home improvement stores had a sale on ceiling fans that I wanted to take advantage of, because it included a number of Energy Star certified products. I went to the Energy Star Product Finder to look up the performance specifications of the fans that were currently on sale.

Well, the dichotomy between ceiling fans that meet the minimum efficacy levels and ceiling fans that seem light years ahead of those levels is quite remarkable!

The minimum efficacy levels set forth in the product criteria are as follows:

  • At low speed, fans must have a minimum airflow of 1,250 CFM and an efficiency of 155 cfm/W
  • At medium speed, fans must have a minimum airflow of 3,000 CFM and an efficiency of 100 cfm/W
  • At high speed, fans must have a minimum airflow of 5,000 CFM and an efficiency of 75 cfm/W

A ceiling fan sized 43” to 60” meeting the above criteria, in addition to the luminair requirements, will carry the Energy Star label. And most of those fans may exceed those standards by a factor of about 1.3.

Yet there are ceiling fans on the market that leave those requirements in the dust. Take the Emerson Midway Eco (CF955) that I researched and purchased for our 1st floor:

  • At 561 cfm/W at low speed, it is 3.6 times more efficient than the minimum requirement
  • At 475 cfm/W at medium speed, it is 4.75 times more efficient than the minimum requirement
  • At 336 cfm/.W at high speed, it is 4.5 times more efficient that the minimum requirement

On the extreme end, the Home Decorators Collection – 60in Aero Breeze at 1447 cfm/W at low speed, exceeds the minimum requirements by a factor of 9.3.

Bottom line: Look for the Energy star label on products, but don’t buy just yet! Do your research first, because there may be a product that blows those Energy Star requirements out of the water – and saves you money down the road.

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Wet duct insulation!

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.


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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Picking a minisplit

Talking to a lot of people and reading the latest accounts and reports of minisplit models prompted me to eyeball the high efficiency, Energy Star rated Fujitsu models.


Their cooling operation range extends to 115 degrees Fahrenheit, while their heating operating range goes as low as five degree Fahrenheit. Think about this: At an outdoor temperature of five degrees Fahrenheit, this unit can still extract enough thermal energy out of the air to heat the inside of the building. The magic of physics!

The big question, however, revolved around cooling rather than heating. I still had to determine the actual cooling load of our first floor. The Fujitsu models came at a cooling capacity of 9,000, 12,000 and 14,500 Btu. With the help of Eco Achievers, we re-ran the energy model for the building to determined an actual cooling load of 12,000 Btu for the 1st floor.

This made the 12,000 Btu minisplit (12RLS3) a perfect match. It has a SEER rating of 29.3 and a moisture removal capacity of up to 2.7 pints per hour. I would have loved to get away with the 9,000 Btu model at a SEER of 33, but that bar was set too high for us.

I was also told that these units run extremely quietly. That was very important to me. I despise the sound of an air conditioning unit humming away during the summer. Plus, our outdoor unit will be mounted on the east wall of our building where it is fairly close to some windows.

It also comes with other bells and whistles which probably deserve their own blog post. But I first want the minisplit installed and running so that I can report back on its performance.

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Wait and see

When it came to cooling options, some ideas were left in the dust, such as:

The viable options that remained were:

Cathy and I wanted to see what our cooling needs on the 1st floor really were. So we decided on a wait-and-see approach: “Let’s live a summer or two in our deep energy retrofit without system air conditioning and see how bad it gets.” That also bought me extra time to come up with some more cool ideas.

Our wait-and-see experiment over the past two years did not yield any surprises. There are summer days where air conditioning is essential, despite our thorough deep energy retrofit. And with climate change barreling down on us, it would be wise to assume that the number of those hot days will increase.

But we also found out that it doesn’t take much air conditioning to keep reasonably cool. We had used a portable 8,000 Btu Energy Star AC when it became unbearable, and it did a decent job, even in keeping the relative humidity down.


I used this time to follow the development on the “Magic Boxes” – energy or heat recovery ventilators (ERV or HRV) with an integrated air-to-air heat pump. I also put this question on the GreenBuildingAdvisor.com Q&A secion: Would the Magic Box be a good alternative to the minisplit in combination with our ERV?

The answer was an unambiguous no!

Dana Dorsett, a frequent contributor to the forums pointed out that “…ERV/HRV air volumes are too low, with temperature differences too small to make them useful for distributing heat/cool.”

Furthermore, Dana pointed to the difference in cooling efficiency. Where a Magic Box may deliver a mere Seasonal Energy Efficiency Ratio (SEER) of 11, an efficient minisplit could have an impressive SEER 33.

This finally pushed me over the edge and I felt comfortable going with the most frequent recommendation: Using a minisplit in combination with our ERV to provide the needed summer cooling and dehumidification.

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Mini what?

We had options, but that didn’t make the decision about how to stay cool any easier.

I could eliminate an air-to-water heat pump because of cost. Martin Holladay at GreenBuildingAdvisor.com said it well: “The cost of these appliances is so high that it’s more economical to buy three separate appliances: an HRV, a water heater, and a ductless minisplit heat-pump.”

An ERV (Energy Recovery Ventilator) with a right sized integrated air-to-air heat pump could work, though.

One should ask for help when it’s needed, so I turned to some green building experts to assist me in the decision making process. The recommendation was to use a minisplit in combination with our ERV to meet our cooling and ventilation needs. And I have come across the same recommendation over and over again, implicitly or explicitly, like in the quote above by Martin Holladay.

What is a minisplit

It is an air-source heat pump that is split into an outdoor condenser and indoor evaporator – thus the split in the minisplit. It is very similar to a conventional AC system, which also has an outdoor condenser and indoor evaporator, but with two important differences.

The minisplit does not require duct work but instead has a wall mounted cassette, which accommodates the indoor evaporator and blower fan.


The minisplit has a expansion and check valve set up that allows for cooling during the summer months. But those valves can be switched, in which case the unit provides heating during the cold season.

How can that be?

The evaporator can be turned into a condenser and vise versa. This requires a reversing valve in the outdoor unit along with the option to switch between a bypass and expansion valve in both the indoor and outdoor units.

During cooling mode, a compressor in the outdoor unit takes the hot, low pressure refrigerant vapor and converts it into hot, high pressure refrigerant vapor. That hot, high pressure vapor is routed to the coil of the outside unit, which acts as a condenser. The coil is cooled by a fan blowing outside air over it. This cooling removes heat from the refrigerant and allows for a phase change – from vapor to liquid. In other words, the hot high pressure vapor condenses into a cooler, high pressure liquid refrigerant, which is now pumped to the indoor unit.

The indoor unit has an expansion valve and heat exchanger coil with a fan. Here the coil acts as a evaporator: the expansion valve allows the cooler, high pressure liquid refrigerant to evaporate into low pressure vapor. This phase change is the reverse from that of the outside condenser. The phase change (from liquid to vapor) requires heat. That heat is extracted from the indoor air, which is blown over the coil (heat exchanger). Once the air passed over the coil, it is cooled and dehumidified, because excess humidity condenses on the cold coil.

The now hot, low pressure refrigerant vapor is traveling back to the compressor in the outdoor unit where the cycle repeats itself.

In heating mode a reversing valve turns the refrigerant flow around. The expansion valve in the outdoor unit is activated, turning the coil into an evaporator, and in the process absorbing heat from the outside air. The hot refrigerant is pumped to the indoor unit, where it bypasses the expansion valve and turns the indoor coil into a condenser, where heat from the phase change is used to heat the building.

Still confused? I don’t blame you! Here is a link to a Youtube video that I found. It shows how a minisplit heat pump works.

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Cool ideas?

ERV – keeping the heat

1st floor ventilation planning

Picking an ERV

Summer heat or summer freeze

Heat wave