Party Walls

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.

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.”

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.

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.

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.

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).

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.

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.

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.

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.

A few months ago I wrote about air-source heat pumps (ASHPs) in cold climates, and I promised more info on how to select the right systems and get the best performance. Below are some things we’ve learned from our work with ASHPs in the Northeast; much of this is based on the results from a study supported by the DOE Building America program. To be clear, we’re talking about inverter-driven (variable-speed) heat pumps in residential applications during heating season. Cooling is certainly important also, but we’ve been more focused on the heating performance, especially at lower temperatures. (more…)

In the first two entries of this series (Part One | Part Two), we explored advanced controls for electrically heated buildings; combined heat and power systems; upgraded atmospheric boilers and ventilation systems. For the final installment of SWA’s Favorite Multifamily Retrofits, we’ll examine the ins-and-outs of stand-alone energy storage. (more…)

Earlier this year, at the AHR Expo in Orlando, the biggest trade show for HVAC professionals, Aeroseal’s duct sealing technology was declared the Product of the Year, the top honor of the Innovation Awards. Aeroseal was recognized as “a groundbreaking solution to an industry-wide problem.”

The unique appeal of the Aeroseal technology is that it seals ducts from the inside. Walls and ceilings do not need to be removed or damaged to gain access for traditional mastic sealing. Aerosolized vinyl polymer particles from 2 to 20 micrometers are injected into a pressurized duct system. The particles stay suspended in the air stream until they reach the leaks, where they are deposited and built up at the leak edges until the leaks are sealed.

The Aeroseal technology has been around for more than two decades. It was developed at Lawrence Berkeley National Laboratory in the early nineties and patented in 1997. It has received many awards over the years including the Best of What’s New award from Popular Science magazine in 1996 and the Energy 100 award from the U.S. Department of Energy.

So what’s the big deal?

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In our first entry of this three-part series, we described advanced controls for electrically heated buildings, combined heat and power systems, and upgraded atmospheric boilers. This time around, we’ll examine the ins-and-outs of exhaust ventilation in multifamily buildings. (more…)

I’ll save the long-winded introduction and get straight to the facts. Based on New York City’s publicly available Local Law 84 (LL84) benchmarking data for 2015, hotels emit 32% more greenhouse gas (GHG) per square foot than the average for all buildings. I also want to qualify this by making a few statements about the data:

1. There are 13,973 buildings on the Department of Finance list; of which 2,353 did not comply with LL84 or are not required to comply.
2. We removed the outliers. Weather-normalized source energy use intensity (EUI) over 550 and under 100 (kBtu/ft2) typically indicates erroneous data. Most likely either the building’s benchmarking activities or report filed with NYC were completed incorrectly.
3. A significant portion of the list comprises the buildings with erroneous data: 4950. Seems a little crazy, no? Leaving us with a good topic for another day….
4. For clarity, that means we analyzed the remaining 6,654 buildings.

The good news – for the sake of this post – is that the hotel market had one of the higher rates of correctly reported compliance data. Out of 187 buildings, 143 reported with numbers that were in a normal range. The average for the sector however, reflects EUI and GHG emissions per square foot that are much higher than other similar building types. Multifamily buildings, for example, have an average of 42% lower GHG emissions/ft2 than hotels (see table below). (more…)

There is no single retrofit that is a panacea for all multifamily buildings. There are myriad options and permutations for upgrades, the efficacy of which is defined by the operational needs, budget, and goals set by the owner. With that in mind, we will examine six retrofits popular with SWA clients in this three-part blog series. (more…)

Air-source heat pumps are a booming business. In the Northeast, manufacturers report that sales of residential systems have increased by 25-35% per year over the past 5-10 years. We’ve seen more and more systems being installed in existing homes (to provide cooling while offsetting oil or propane used for heating) and into new homes (often as the sole source of heating and cooling).

We’ve looked into these systems often, and from many perspectives. I’m planning a series of posts, but, for now, here are the answers to some basic questions we receive from clients.

First, the basics: What is an air-source heat pump (ASHP)?

It’s an air conditioner that can operate in reverse. During the summer, it moves heat from indoors to outdoors. In the winter, it moves heat from outdoors to indoors. We helped NEEP (the Northeast Energy Efficiency Partnerships) to put together a market assessment and strategy report on ASHPs. The early sections in this document (see p. 12) outline the different terms and types of heat pumps (ducted/ductless, split/packaged, mini-split, multi-split, central, etc.) Unfortunately, different people can use the same term to mean different things, but hopefully the NEEP Northeast/Mid-Atlantic Air-Source Heat Pump Strategies Report can help clarify things.

 

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Do you live in DC? Do you own, manage or reside in a multifamily building? If so, we would love to get your feedback!

The District of Columbia’s Department of Energy and Environment (DOEE) has engaged Steven Winter Associates to gain feedback from multifamily owners, managers and residents about their energy and water usage. To start off, we’re conducting brief surveys (10-minutes max), and hope this effort will have positive outcomes for future multifamily projects in DC by raising awareness of green/energy efficiency initiatives.

PURPOSE:
Survey responses will inform the potential development of a voluntary energy and water conservation program tailored exclusively for the multifamily rental sector in the District. This program will include a customized toolkit to engage residents and building managers in improving energy and water efficiency. It will also encourage participation in a peer-to-peer energy and water reduction competition.

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Last week, I had the opportunity to visit the DURAhome, New York City College of Technology’s entry for the 2015 Solar Decathlon. This project is currently nearing completion at the Brooklyn Navy Yard. Over the past 3 months, more than sixty students have toiled around the clock to finish construction in time for the contest, which will take place October 8-18 in Irvine, California. The Solar Decathlon is the U.S. Department of Energy’s biennial competition that challenges college and university student-led teams to design and build solar-powered net-zero homes that are affordable, energy-efficient, and aesthetically appealing.

TeamDURA’s focus was to create a prototype of post-disaster housing that is suited for New York City’s high-density urban environment, and could serve as a shelter in the aftermath of a catastrophic storm. As such, multifamily, multistory solutions were preferable to traditional single-family trailers, which have larger footprints. DURAhome consists of several prefabricated modules that can be packaged and shipped on standard-sized tractor trailers for quick response at low cost. These flexible modules can then be joined in standalone configurations or stacked for multifamily uses. Like the city, the DURAhome is diverse, urban, resilient, and adaptable.

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