Party Walls

Steam pressure gets a disproportionate amount of attention. That’s partially due to the common, but not necessarily true idea that higher pressure equals more fuel use. Remember, it’s not the steam’s pressure that heats the building; it’s the steam’s heat energy. In fact, you can heat a building with 0 psig steam. You can even heat a building with a boiler that’s too small and never builds positive pressure. You can’t do it well, but you can do it.

System Operation

Thanks to the law of conservation of energy, we know that energy cannot be created or destroyed — it can only be altered from one form to another. In a steam heating system, the flow of energy goes like this:

1. The boiler transfers Btus from the fuel to the steam (energy input).
2. The steam transfers those Btus to the rooms.
3. The rooms transfer those Btus to the outdoors (heat loss, aka the load).

It’s important to keep this energy flow in mind because they are linked and self-equalizing. If the energy input exceeds the heat loss, the building temperature will increase, which, in turn, increases the heat loss. And, a building’s heat loss depends on the temperature difference between inside and outside and the amount of air transfer occurring. So, the best way to keep the heat loss down is to keep the indoor temperatures as low as possible, and keep the windows closed. Furthermore, in an apartment building, the coldest room drives the load in any steam-heated building and the Super needs to send enough heat around to satisfy the hardest-to-heat apartment.

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Residential ventilation is really a tricky topic. But if you’re looking for a practical, cost-effective, holistic solution, go somewhere else. This post offers none.

Hopefully I can dig into practical solutions in future posts, but I think it’s important to be clear about why we ventilate and what an “ideal” ventilation system might look like in a new, efficient home. My ideal system is similar for both single-family or multi-family (though practical issues can be very, very different).

Purpose of ventilation: Remove contaminants that can compromise health, comfort, productivity, durability, etc. I’m sure there are more rigorous definitions out there, but this will work for now. There are other ways to lower contaminant levels:

• Emitting fewer contaminants from materials and activities is obviously good. Do this.
• Actively filtering, adsorbing, or otherwise removing contaminants from indoor air can also be good. There’s talk about doing more of this, but I’m tabling it for this discussion. This may be something to keep an eye on down the road.

For most new residential buildings, mechanical ventilation is still be the primary means to remove contaminants. Or at least it’s the primary method that designers/developers need to plan for now.

If building a new, efficient home in Shangri-La, my ideal ventilation systems would look like this: (more…)

The International Energy Conservation Code (IECC) has a number of requirements involving energy recovery on ventilation systems. Requirements vary based on climate zone, building type and size, equipment capacity, and equipment operating hours. As a result, many new construction projects must now incorporate energy recovery considerations into their design.

An energy recovery unit (ERU) equipped with a heat wheel can be a great way to satisfy these energy recovery requirements. The ERU can be a roof-mounted air handling unit, or can be an air handling unit located inside a mechanical room with outdoor air and exhaust streams ducted in. The heat wheel is positioned so that half of the wheel sits in the exhaust air duct and the other half sits in the outdoor air intake duct. During cold weather, the wheel spins, transferring heat from the exhaust stream to the outdoor air intake stream. During hot weather, the wheel transfers heat from the outdoor air intake stream to the exhaust stream. In both cases the heat exchange enables the building to take advantage of the more comfortable conditions of the exhaust air, while still allowing fresh air to enter the building. During extreme weather conditions, heat wheels can save energy on space conditioning while still allowing for healthy indoor air quality.
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As seen in:

• Spring 2018 edition of BuildingEnergy Magazine (NESEA)
•  August 2017 edition of Green Energy Times

Humans have been trying to harness the power of the sun for millennia. The advent and popularization of photovoltaics in the latter half of the twentieth century made doing so accessible to the masses. Today, solar arrays are commonly seen adorning the roofs of suburban homes and “big-box” retailers, as well as on other landscapes including expansive solar farms and capped landfills. Until recently, the common thread amongst these locations has been the employment of open space. Solar applications have historically been reserved for use in areas of low-to-moderate building density.

By the end of 2050, solar energy is projected to be the world’s largest source of electricity. While utility-scale solar will comprise the majority of this capacity, there will also be significant growth in the commercial and residential sectors – particularly in cities. Industry influencers are increasingly focused on creating opportunities for solar applications in high-density areas, where much of the demand lies.

In their 2014 Technological Roadmaps for solar PV and solar thermal electricity (STE), the International Energy Agency (IEA) predicts Solar PV and STE to represent over 25% of global electricity generation by 2050.

 

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About a year ago, I worked along with other HERS raters and the North American Insulation Manufacturers Association (NAIMA, a.k.a. Insulation Institute) to conduct a study on the importance of insulation installation quality and grading.

RESNET, the nation’s leading home energy efficiency network and the governing body of the Home Energy Rating System (HERS® Index) established standards for grading insulation installation.

The grading is as follows:

Grade I— the best and nearly perfect install which includes almost no gaps or compression… what some would call “G.O.A.T.”
Grade II—allows for up to 2% of missing insulation (gaps) and up to 10% compression over the insulation surface area… what some would call “mad decent”.
Grade III—insulation gaps exceed 2% and compression exceeds 10%… anything worse and the insulated surface area is considered un-insulated.

Source: RESNET Mortgage Industry National HERS Standards

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Variable refrigerant flow (VRF), also known as variable refrigerant volume, was a concept developed by Daikin Industries in the 1980s. The technology is based on transferring heat through refrigerant lines from an outdoor compressor to multiple indoor fan coil units. VRF systems vary the amount of refrigerant delivered to each indoor unit based on demand, typically through variable speed drives (VFDs) and electronic expansion valves (EEVs). This technology differs from conventional HVAC systems in which airflow is varied based on changes in the thermal load of the space.

The two main VRF systems are heat pump systems that deliver either heating or cooling, or heat recovery systems that can provide simultaneous heating and cooling. These two applications, plus the inverter-driven technology of the outdoor compressors, allow for greater design flexibility and energy savings. In applications where heating and cooling are simultaneously called for in different zones, VRF heat recovery systems allow heat rejected from spaces that are being cooled to be used in spaces where heating is desired. (more…)

New York City has established high goals for CO₂ reductions as part of the 80 x 50 plan enacted under Mayor de Blasio’s administration. In short, NYC aims to reduce its CO₂ production by at least 80% by 2050 (from a 2005 baseline). This requires vast energy conservation and renewable energy production proliferation across the city’s energy, transportation, waste management, and building sectors. Buildings themselves account for 68% of current CO₂ production in the City, and as such have the largest reduction targets¹. Goals can only be met by implementing repeatable and scalable scopes of work in coordination with policy updates and improvements in other energy sectors. To better understand the efficacy of these moderate improvements on overall energy consumption, we’ve analyzed the results from a recent portfolio rehabilitation. These findings help us to create a map of where we need to go in order to approach 80 X 50.

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What is Commissioning?

Many energy and sustainability programs, standards, and codes require commissioning, including LEED, ASHRAE 90.1, NGBS, IECC, IGCC, the PSEG and NYSERDA’s commercial performance-based incentive programs (see glossary below). As states embrace these codes and enforce commissioning requirements you may ask yourself: what is commissioning and why is it beneficial?

Commissioning agents provide third-party quality assurance throughout the construction process. They review design drawings and submittals, periodically inspect construction progress, witness functional performance testing of mechanical equipment, and ensure that the building staff is trained and ready to operate the equipment after it’s turned over. Commissioning agents work on behalf of the owner to ensure that the owner’s project requirements are met. Most importantly, commissioning improves construction quality and reduces maintenance and energy costs.

The benefits of commissioning are never more apparent than during a retro-commissioning project. While commissioning involves a third-party review of operation during the construction process, retro-commissioning is a third-party review of operations well after construction is complete. Some difficult retro-commissioning projects have shown us how valuable it is to resolve issues when the design intent is still clear (or clearer) – and while the construction team is still onsite!

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Winter in the City

Wintertime in New York City: cold wind whips down the avenue and seems to follow you as you leave the frozen street and enter your building. The cold gust pulls the heat out of the lobby and even seems to follow you as you make your way up the building, whistling through the elevator shaft as it goes. The colder it gets outside, the worse it gets inside. Can’t somebody please make it stop? Is it too much to ask to be comfortable in your own lobby?

No, it is not too much to ask, and yes, we can help. It is 2016 and we have the technologies and expertise to better manage this all-too-common problem, but first we must examine what forces lay at the heart of the issue.

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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.