How Effective is that Range Hood?

Next time you are cooking, take a look at your kitchen hood. You are likely cooking on the front two burners, but your kitchen hood is not likely to extend fully over these burners. For typical exhaust fans, they do a good job of exhausting steam, contaminants, etc. from directly below them, but don’t necessarily pull all fumes that are outside the perimeter of the fan enclosure.  According to Lawrence Berkeley National Laboratory (LBNL) the capture efficiency of standard hoods is typically in the range of 30-40% on front burners and can be as high as 90% on back burners. To demonstrate this, I boiled some water in a tea pot on my stove. Once steam was coming out, I pulled out an infrared camera and started to take images. Wait…you don’t have an IR camera just sitting around your home? You are missing out on hours and hours of fun with the kids. They are great for science projects.

Back to my point. I have an LG over-the-range microwave with extenda™ vent. This allows the vent area to extend out an additional ~6”. When the microwave hood (exhausted to outside) was operating on turbo mode (just over 300 cfm exhaust) and without the vent extension slid out, the majority of steam from the tea pot on the front burner was passing by the vent and going up the front of the microwave (as evidenced by moisture build up on the microwave door). And yes, I realize that I turned the spout of the tea pot outwards to more dramatically show the point I am trying to make. When the slide out vent was pulled out, the amount of steam capture increased dramatically, but there was still some moisture build up on the front edge of the vent slide out.  Obviously, this is not a scientific study; it is just anecdotal evidence to further the discussion on the need to consider capture efficiency in the design of kitchen range hoods.

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Figure 1. (Left) IR image of steam from a tea pot bypassing vent hood without hood extension slide out. (Center) Picture of range and hood setup with hood extension slide out. (Right) IR image of steam from a tea pot mostly being captured by vent hood with hood extension slide out.

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It’s 2016. Do You Know What’s Going Into the 2018 IECC?

By Gayathri Vijayakumar, VP Senior Building Systems Engineer

New Energy Code on the Horizon?ICC_Logo_Vert_PMS_7729

We’re already more than halfway through 2016, and many states are still enforcing energy codes from 2009. While a few have adopted 2012 IECC and even 2015 IECC, state adoption of energy codes tends to remain a few years behind the times and the code development process continues. In fact, the wheels are in motion to create the 2018 IECC. Hundreds of proposed changes were submitted and reviewed early this year.

Based upon the Committee Action Hearing in April, some proposed changes were preliminarily approved and some weren’t. The Public Comment period occurred in July, providing an opportunity for others to weigh in. So, while the 2018 IECC may not affect projects for years to come, SWA weighed in, advocating for changes we think would be good additions to the 2018 IECC.

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Air-Source Heat Pumps in Cold Climates (Part III): Outdoor Units

I’ve talked a little bit about new, air-source heat pumps (ASHPs) in older posts (I, II). There are some newer products that can work really well in cold climates, but proper sizing, installation, and operation are critical for getting good performance. One key factor is proper location of outdoor units.

First, a bit of nomenclature. The part of a split air conditioner that goes outside is often called the “condensing unit.” It usually contains most of the key refrigeration components: the compressor, condenser, expansion device, etc. The only key component located inside is the evaporator coil: where the refrigerant evaporates as it removes heat from the indoor air.

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In a heat pump, all this is still true during the summer. During heating season, however, the condenser is indoors (releasing heat to the indoor air stream) and the evaporator is outdoors (removing heat from outdoor air). Because of this, calling the outdoor unit a “condensing unit” isn’t quite correct. People still use this term for a heat pump, but I think more people are simply calling it the “outdoor unit.”

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During the winter, the outdoor unit removes heat from air blowing through it. Here then, is the key point to remember:  If the outdoor unit is encased in snow and ice, it is not able to remove heat from the air. Obvious, yes? But it’s amazing how often there are lapses in this.

This image below is of a new, all-electric home, and this heat pump is the primary heating system. If this was simply an air conditioner, there’d be no problem. But this is located directly beneath the gutter-less drip edge of the roof. A lot of rain and melting snow and ice is going to fall on this heat pump. When this moisture hits the evaporator coil, it will freeze. This is a new home in Maine; I expect problems.

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Heat pumps have built-in defrost mechanisms, as some coil freezing is to be expected. However, when heat pumps are subject to extraordinary levels of moisture, the systems defrost A LOT. When doing testing for our study, we ran into this problem in several homes. The heat pump below was beneath a deck; it was protected from direct snow, but as snow on the deck melted, water dripped onto the heat pump where it froze. This heat pump only ran for 10 minutes before it needed to defrost again (run for 10 minutes, defrost for 7 minutes, run for 10 minutes, defrost for 7 minutes…). This is not good. Defrost cycles don’t generally use a tremendous amount of energy, but they usually happen only once every hour or so. If the system is in defrost mode ~41% of the time (7 of 17 minutes), it has at least 41% less capacity.

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Drip edges from roofs are pretty obvious, but the snow melt from the deck was a less obvious source of moisture. One other source of moisture that has surprised me is other heat pumps. This is obvious in hindsight, but when heat pumps defrost, there’s liquid water that usually just drips out. What happens if there’s another heat pump below? Or three heat pumps? Before some corrective measures were taken in the installation below, the bottom heat pump really had problems – cumulative ice from the three heat pumps above it defrosting.

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But this stacked, wall-mounted configuration was really efficient and convenient for this building; what to do? At this building, the owner installed piping to drain away moisture from defrost cycles (pic below). I was concerned that the ice just might freeze and block these pipes, but that hasn’t happened (and this building has been through one very cold, snowy winter).

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I think a more simple solution is a cover. The heat pump below had a simple, site built-cover. It worked fine. Observe also that the unit is on a little pad and some blocks to keep it up out of the snow.

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The blocks and pad get it ~12” above the ground. What happens if there is more than 12” of snow? Like maybe five feet? The answer is pretty straightforward: either the heat pump stops working or someone needs to do a lot of shoveling. Here they did a lot of shoveling. You may not be able to tell, but the picture above and below are of the same heat pump. Granted, this was during the record-breaking snowfall in Massachusetts two winters ago (2014-15), but there’s no sense in increasing snow shoveling loads.

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So below I think is a great solution. These heat pump outdoor units are NOT located beneath a drip edge or other moisture source, but they still have covers on them for good measure. And they’re 4-5 feet off the ground. This home is in Maine where these heat pump “hats” have become pretty common. Some heat pump distributors have contracted with sheet metal fabricators to make hats for common heat pump models.

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I think the installation shown above is great, but this may not be appropriate for all buildings. I’ve heard some stories of heat pumps mounted on wall brackets where vibrations from the heat pumps carry through the building. I’ve not seen this in any projects I’ve worked on – in my experience the outdoor units are very quiet and the vibrations are minimal – but others have certainly reported problems. This might be a bigger concern for older, 2×4 framed buildings. The home above has double 2×4 walls with exterior rigid foam – lots of vibration dampening. If vibrations from wall mounting are a concern, try to use stands to keep the outdoor units well above snow height.

The Future is Here: NYC Adopts New Energy Code

With a New York City Council vote on July 14, 2016 NYC adopted amendments to the new New York State (NYS) energy code, which go live October 3rd of this year. Since any amendments to the state code must technically be of greater stringency, there are some notable additions. In this article we NYC Cityscapewill discuss the highlights of both the new NYS and NYC energy code versions for commercial construction (includes multifamily above 3-stories) and what to expect in upcoming revisions as the bar is raised on energy efficiency and high performance buildings.

Before we discuss the highlights, here is a quick primer on the underlying basis of the new code. The new NYS energy code also known as New York State Energy Conservation Construction Code (NYSECCC) is based on a model code and standard – 2015 International Energy Conservation Code (IECC) and ASHRAE 90.1-2013. Naturally, the NYSECC is then referred to as 2015 IECC + 2016 NYS Supplement. In NYC, it’s simply 2016 NYCECC. Got it?

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The Reasons Behind the Requirements

Written by Theresa D’Andrea, Accessibility Specialist

This month, several members of the Accessibility Team had the unique opportunity to experience navigating architectural barriers commonly faced by people who use wheelchairs. We attended a seminar held in New Jersey that involved actually getting into a wheelchair and going through a series of obstacles to experience just how challenging it is to navigate environments that do not meet (or just barely meet) the minimum standards of accessibility compliance. The experience of using a wheelchair to negotiate common obstacles brought to light the rationale behind accessible design and construction requirements that we deal with on a daily basis.
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