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Notes from Abroad: A SWArrior in Sweden

In October, NESEA awarded SWA’s Heather Nolen with a travel scholarship through the Kate Goldstein Fund for Emerging Professionals (you can read the announcement here). Heather joined four other scholarship recipients for a two week  journey to Denmark and Sweden to explore  innovative sustainability methods being used in their buildings. The following is blog entry written by Heather, describing her experience at a location outside of Stockholm. (This entry was reblogged from NESEA’s blog; you can find the original post here.)

We met with Björn Cederquist who was kind enough to tell us about Hammarby Sjöstad, a new sustainable district, which he is quite proud of.

Stockholm is a growing city, with a population of 1.5 million and a serious lack of housing. The city central is quite developed, outside the city there are the typical suburbs, it is the area between the city proper and the suburbs that Stockholm is looking to develop in a planned, sustainable manner. To meet the city’s housing needs Stockholm plans to construct 8,000 units per year, mind you they have only been building at 5,000 units/year of maximum. This is a large undertaking for the city which is being planned in a thoughtful way.

Despite the need for more units of housing there is a strong tradition in Stockholm of midrise buildings which accounts for the reluctance to build higher. Hammarby Sjöstad is mostly mid-rise with one exception, a single 12 story building.

Located in this prime area between the city and suburbs, Hammarby Sjöstad is located at an old harbor and landfill turned Brownfield site. To convert this piece of land into a residential community public transportation had to be extended, both the subway and train lines. The presence of transit shows a commitment to the area, a feeling of permanence which is required to build the community. 80% of residents commute by public transit.

To meet sustainability goals in a comprehensive way the district aimed to be a healthy place for people to live that stimulates the body and soul with opportunities for exercise, sports and culture. Design began in 1990 to construct an “Environmental and Ecological City District,” which includes 11,000 units housing over 25,000 people; an additional 10,000 are projected to work within this area. In addition to the housing and transit systems, power plants were constructed to provide district heating and cooling, waste removal including organic waste, public water supply and wastewater treatment.

Renewable energy sources, harvesting of energy from the areas wastewater system, burning of waste combustibles along with harvesting energy from the sewage system allow Hammarby Sjöstad to operate their CHP plant free of fossil fuels. Central heat pumps at the district plant operate year round to extract energy which allows for district cooling, planned for 10 years the plant is the largest in the world. The wastewater treatment plant harvests both bio-gas and bio-solids. Bio-gas is used to power buses, taxis and some individual stoves. Bio-solids are used as fertilizer in forest, filling mines and soon to be used for agriculture purposed. Combined with advanced waste collection and energy efficient construction Hammarby Sjöstad is a unique community which is a product of long-term planning and collaboration. Sites underdevelopment are learning from Ham Hammarby Sjöstad to further advance eco-districts for long-term success.

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Survey says.. Feedback is Fundamental.

While commissioning and utility metering provide quantitative building performance data, post-occupancy surveying qualitatively gauges tenant awareness, understanding, and appreciation of green features. Forego this step, and you miss a critical opportunity to engage end-users in the green building experience.

Recently, SWA launched an initiative to collect post-occupancy evaluations from certified projects. University Village on Colvin (LEED® for Homes™ Gold-certified, Syracuse off-campus housing) was the first to participate.

PartyWalls_UnivHousColvin

Key Survey Findings from University Village Residents:
• 94% of respondents reported being conscious of energy and water conservation
• 77% of respondents were satisfied with the green features of the buildings. Green features were defined as those that save energy, water and natural resources, and promote indoor environmental quality.
• Favorite green features among the respondents were: air conditioning, recycling accessibility, low-flow shower and aerator, and ENERGY STAR® appliances
• 94% of respondents reported satisfaction with the general building site maintenance

Surveying is an essential touch-point coupling building, management, and resident. It forces both stakeholder groups to assess their relationship with the sustainably built environment. At University Village, tenants took stock of their green living area, assigned a personal value to green features, and considered ecological impacts of their behavior. In turn, property managers can discern how their investment translates to improved quality of life, which elements of their investment carry added marketability for luring prospective tenants, and how residents interact with green features to either maximize or minimize their usefulness.

Post-occupancy surveying humanizes green building through education and exposure, demystifying what would otherwise be overly esoteric or easily overlooked technology. In an industry largely under-discussed by a green-ho public, a simple measure that improves accessibility and relatability of green building is invaluable to mainstreaming our beloved practice.

Energy Codes: Who Needs ‘Em?

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Energy Code. We could use that term for many things: how you feel after a cup of coffee, before a dreaded workout, or even at 2am when you’re staring at your bedroom ceiling knowing you have to be up in 4 hours. But here we’re talking about buildings, specifically in NYC.

Apparently, nine out of every 10 buildings have failed to meet the energy code, a set of standards that have been in place for a whopping 30 years. Crain’s New York published an article about it, featuring the NYC DOB’s audit results of thousands of architectural plans for new and renovated office and residential buildings.

Worried that your building might fail? Don’t fret, SWA’s in-house energy code expert, Michael O’Donnell, answered a few questions for us. Get the low down on what the energy code is all about and what these results mean.

Party Walls: So tell us, what is the energy code? And what (or who) brought about the need to enforce an energy code?
Michael O’Donnell: The energy code contains the minimum requirements that buildings must meet with regards to energy efficiency measures. According to the Department of Buildings, to meet the City’s goal of reducing greenhouse emissions by 30% by 2030, the New York City Energy Conservation Code (NYCECC) sets energy-efficiency standards for new construction, alterations, and changes to existing buildings. All new building and alteration applications filed on or after December 28, 2010 must comply with the 2011 edition of the NYCECC. The need to for an energy code has been around for many years but it is only really being enforced relatively recently.

PW: What are the benefits of a building meeting the energy code?
MO: Buildings that effectively meet the energy code will be better insulated, have better HVAC systems, and better lighting systems. As these systems are designed, implemented, and optimized, reduced operating costs for both owners and tenants will result. There are also environmental benefits of reducing greenhouse gas emissions achieved by utilizing less electricity and/or heating fuel.

PW: What are the potential risks of not meeting the energy code standards?
MO: Potential risks of not meeting the energy code include tenant comfort complaints, higher operating costs for electricity and/or heating fuel, and, more recently, action by the Department of Buildings. Energy code audits of building plans have the potential to stop a project in its tracks as well as impose fines for constructed buildings that are not meeting the code.

PW: What are the biggest reasons buildings fail to meet the energy code?
MO: There are a few reasons buildings fail to meet the energy code. Specific details are often missed or not included in the construction drawings and specifications. If details are not included, the contractor will not incorporate these items into what actually gets built. Even if specific energy related items are incorporated, the contractor may not have the knowledge to properly install or execute what is shown. Finally, it takes a trained inspector to know what to look for to ensure buildings are compliant with energy code. NYC requires the large majority of projects to file a “TR8: Technical Report Statement of Responsibility for Energy Code Progress Inspections” form through which a licensed architect or engineer takes the responsibility of inspecting for energy code compliance. This form is required in NYC, but other jurisdictions, which do not require the progress inspection run the risk of having items overlooked or missed since there is not a third party inspecting specifically for energy code items.

Read the Crain’s New York article here:
http://www.crainsnewyork.com/article/20140818/REAL_ESTATE/308179994/9-of-10-building-plans-fail-basic-test

Greenbuild Recap: Steven Winter Talks Building Science

As part of Hanley Wood’s Vision 2020 Sustainability Council, Steven Winter presented his thoughts on how building science can have a big impact on meeting 2020 energy efficiency targets.  The presentation took place on the first day of Greenbuild 2014 (10/22) in NOLA. (I should write out the city’s proper name, but it’s a fun acronym that I don’t often get to use!)

Some great themes to watch for: Thinking about large-scale impacts, the role that new technology will play, how to motivate change.

 

So, carrots or sticks? What do you think’s more effective?

Get This: Engineer Runs House with Car!

Gayathri Vijayakumar, a seasoned Buildings Systems Engineer at SWA ,took a unique precaution against future electrical power outages…

Gayathri connected her Toyota Prius to her New Haven home’s power system.

Gayathri and her Prius

How did she do that?

Gayathri took a special inverter and connected it to her hybrid car, which created a generator. This distinctive system works by connecting the inverter to a transfer switch and starting the Prius, generating enough electricity (1600 Watts) to run the critical circuits in her house, including pre-selected lights, refrigerator, and the electric ignition to the tankless gas water heater.

The inverter, purchased from ConVerdant Vehicles, was less expensive than a standard gas generator, provides electricity by using half the fuel, and is much quieter.

Inverter

 “We were not prepared for our first power outage in Connecticut, but we were able to use the gas stove for cooking and our gas fireplace kept the first floor at well over 70F. Being without a fridge and hot water was a challenge though. Now that we have the Prius, at $4/gallon of gas, generating electricity through the inverter is still more than twice as expensive as buying it from the utility. But in a power outage situation, being able to provide basic power for three days on one tank of gas is pretty amazing” said Gayathri.

Mother Nature is showing us that even though it is critical to focus on energy-efficient building designs and renewable systems, we must include storm resiliency as another component of designing truly sustainable buildings.

Have you taken any unique precautions to protect your home/building against future storms?

Engineering – It’s Not Just a Job, It’s a Lifestyle

Having been in the energy efficiency industry for over a decade, it was always a sore point when SWA’s senior engineer, Srikanth Puttagunta, talked about his own home.  Built in 2003, the townhome was energy inefficient and uncomfortable. With the thermostats set at 70°, temperatures in individual rooms could be 5-10° colder or warmer than the setpoint.

What was the best solution?

Moving. This past year Sri purchased an older split-level home with upgrades to the kitchen and bathrooms. But, it was still energy inefficient. With the help of trusted SWA collaborators Preferred Builders Inc. and Controlled Temperatures Inc., Sri followed the same advice he’d been giving all these years.

Steps to Energy Efficiency

The first step was to insulate and air seal the building shell.  The  old fiberglass batts were removed from the exterior walls (a) prior to dense packing  the wall cavities with cellulose (b), taping all seams in the sheathing (c), installing a drainable housewrap (d), and re-siding (e) with fiber cement siding. After that came air sealing of the roof deck with closed cell spray polyurethane foam (f).

The Perks of Natural Gas

Taking advantage of the availability of natural gas, the old heating system – an oil boiler with an immersion coil for domestic hot water – was replaced with a natural gas, condensing tankless combi-boiler that feeds the existing baseboard radiators and provides domestic hot water.

Keeping it Cool

Cooling was previously provided by a through-wall air conditioner in the kitchen area and window air conditioners in the bedrooms. These were removed and a multi-head mini-split heat pump was installed that provides cooling and supplemental heating. Finally, a 5.2 kW  solar PV system was installed on the roof (g).

The Results

Based on the previous homeowners’ oil and electric bills, energy modeling and testing of the home (73% reduction in air leakage), and initial utility bills since moving in, the upgrades that were performed on this home should result in a nearly 70% reduction in annual energy costs. With about $3,850 per year in savings, the simple payback is less than 15 years. Now that is a home that anyone can be proud of!

Make-Up Air or “Made-Up” Air?

In multifamily buildings, particularly in the Northeast, exhaust ventilation strategies are the norm as a method for meeting both local exhaust and whole-unit mechanical ventilation. We can easily measure that air is exhausted. What we don’t know is where the make-up air is coming from…

Is it “fresh” from outside, from the neighboring apartment, from a pressurized corridor, or the parking garage via the elevator shaft?
Well-intentioned design teams are providing fresh air in many forms, ranging from fully-ducted systems that deliver air directly to apartments, to more passive systems utilizing designed penetrations in the envelope such as trickle vents or fresh air dampers. With funding from DOE’s Building America program, SWA is conducting field research in several multifamily buildings with different types of mechanical ventilation systems to assess how make-up air is provided under the variable pressure conditions that can occur throughout the year.

The Approach
Even though it does not comply with fire codes in at least some jurisdictions, SWA‘s approach is to leave a gap under the apartment door to allow make-up air to enter from the corridor. The general strategy is to pressurize the corridor using outside air and depressurize the apartments through local exhaust. This strategy is being assessed in a 3-story, 78 unit building, where the design called for 5,250 CFM of supply air to the corridors and common areas and a total of 4,980 CFM of exhaust from janitor’s closets, and trash rooms, and continuous exhaust (30-50 CFM) from each apartment.

Measuring the Airflows
In order to extrapolate airflow measurements based on the varying conditions in the building, SWA measured airflows across the apartment door under normal operating conditions for eight apartments. Our team also monitored the pressure differential between the corridor and apartment over a two-week period for five apartments in the building.

Measurement system for determining air flow across door as a function of pressure difference.

Here’s a “Snapshot”
The measurements in the eight apartments showed that while exhaust fans were measured to continuously exhaust 30-40 CFM, the flow into the apartments through the doors ranged from 0 CFM to only 28 CFM. When bathroom exhaust fans in the apartments were activated to their “high” setting ( ~90 CFM each), the flow through the doors increased to an average of 37 CFM, still indicating that a majority of the make-up air is not from the corridor.

The long-term measurements in the five apartments showed airflow across the door into one apartment to max out at 24 CFM. The other four exhibited net airflow from the apartment into the “pressurized” corridor, as much as 40 CFM! Why?! One potential reason: measured supply and exhaust flows in the corridors showed that the supply systems were 25% lower than design and exhaust from the trash rooms was 25% more than design.

Stay tuned for a future post on our findings and recommendations.

Composting with Celeste

Composting

Sustainability Consultant and SWA’s Master Composter, Celeste McMickle, recently lead the workshop, “In-Home Composting” at the GreenHomeNYC Forum. Celeste discussed best practices for at-home (or in-office!) composting, as well as the tools and resources needed for the experienced composter and newbie alike.  For those of us who were unable to attend the workshop, we asked Celeste a few questions about one of her favorite topics.

SWA: What is compost?

CM: Composting is the process of speeding up natural decomposition through science.

SWA: How did you get into composting?

CM: I have always loved gardening and composting is a vital part of the gardening process as it provides nutrients and vitality to the soil and plants. I wanted to learn more and was thrilled to find out about the NYC composting initiatives and wanted to get involved.

SWA:  What are the greatest benefits of composting?

CM: It’s a great way to divert food waste from the overall waste stream. About 40% of household garbage is compostable. Think about what that can do for our ecological footprint, especially as many landfills are at or beyond capacity. We always think of trash and waste as a problem, and I love that compost can be a solution. It’s this marketable desirable product that we can create just be eating the foods we love and choosing to not put them in the landfill.

SWA: How do you use compost?

CM: I’m very fortunate to have a vegetable garden nourished by the compost I make at home (fueled in part by the efforts of team members at SWA!). If you don’t have a garden you can use compost for house plants, street trees, give it to friends, or donate it to a local collection site.

Have you tried composting before?  Let us know what you think!

Can A House Be Too Tight?

 

The Importance of Mechanical Ventilation

During most presentations we give about air sealing and infiltration, like clockwork someone will ask, “but doesn’t the house need to breathe, aren’t we making buildings too tight?” This is a popular green building myth, but  people need to breathe, walls don’t. In fact buildings perform best when they’re air tight and we can temper, filter and regulate the amount of fresh air.

We know the symptoms of poor ventilation – odors, humidity issues, condensation on windows, high levels of chemical off-gassing and even elevated carbon monoxide levels. Some of these effects are immediately apparent to occupants (odors, window condensation) while others may be imperceptible (carbon monoxide). Indoor air quality is a comfort, health and safety concern. However, these problems aren’t necessarily symptoms of tight buildings and can occur in all types of construction, old and new, tight and leaky.

Natural Ventilation Doesn’t Work Anymore

In the past buildings were ventilated with outside air naturally when the wind blew and/or it was cold. If this natural ventilation (or what building professionals call air infiltration) ever worked it doesn’t anymore.

red barn image

“Did you grow up in a barn?” Most of us learned as children the importance of keeping outside air out during heating and cooling seasons. However natural ventilation through building cracks brings unintended moisture and temperature differences that can cause condensation.

 

Old buildings had no insulation or air sealing, so structural failures caused by condensation within a wall assembly rarely occurred. Building codes now require insulation and air sealing which helps lower our energy bills and keep us comfortable inside. But when infiltration happens in a wall full of insulation, condensation can occur on the cool side of the wall assembly, which over time can rot the framing and cause structural issues. This is why it’s critical to prevent air leaks and better understand the thermal boundary.

Americans spend more time in our homes than ever, almost 15 hours per day by some estimates, and humans give off a lot of moisture. While home we tend to keep the windows closed. We’re also seeing increasing amounts of Volatile Organic Compounds (VOCs) emitted from our paints, furniture and household products that are made with chemical compounds that we know little about. For example, solid-wood furniture does not offgass, but plywood, particle board and foam sure do. How much solid wood furniture do you have in your house? Taken together this means there is more moisture, odors and pollutants added to our homes each day than was the case 30 years ago. The EPA estimates indoor pollutants to be 2 to 5 times higher inside homes than outside.Because of all these indoor pollutants, we clearly need to bring fresh outdoor air into the house.

However, the unintentional natural ventilation air our buildings do get rarely comes directly from outside. In the best-case scenario it creeps in through the various cracks in the exterior walls and windows, but most often comes from the least desirable locations shown in the image below: crawlspaces, garages and attics. Leakage from those locations is certainly not “fresh” air. Do you want to breathe in hot dusty attic air, or damp air from your crawlspace? You just might be.

Image of infiltration

Natural ventilation is forced through infiltration points which are most often from the unhealthiest locations in homes

Moreover, unintentional natural ventilation (infiltration) is unreliable and poorly distributed. Infiltration is primarily driven by wind speed and the temperature difference between outdoors and indoors. These weather variables vary day-by-day and season-to-season. For instance, the chart below shows the average conditions for Lancaster, PA. Note the weather fluctuations throughout the year:

  • During summer wind speeds are almost 50% lower
  • The temperature difference is 6-8 times greater during winter

lancaster-weather-conditions chart

These erratic conditions cause the building to be over-ventilated half the time and under-ventilated the other half. Also, infiltration is poorly distributed throughout the house. A room with a couple exterior walls and leaky windows will get far more outside air than an interior kitchen or bathroom. Wind and temperature differences drive ‘natural ventilation’ in the form of infiltration in homes. However these factors are highly variable and unreliable.

To summarize the need for mechanical ventilation:

  • There are more pollutants in our homes than ever, requiring more ventilation air
  • Homes are better insulated and air sealed than they used to be
  • Much of the infiltration that does occur comes from undesirable locations
  • Even the portion of infiltration that can be considered “fresh air” varies sporadically based on weather conditions
  • Having air leaks in an insulated wall, attic or floor assembly can cause condensation and create structural failures.

For all these reasons, relying on air leaks as natural ventilation no longer works. It doesn’t work for normal homes, and it especially doesn’t work for insulated or tight homes.

Build It Tight, Ventilate It Right

The better approach is to provide controlled mechanical ventilation by providing enough air to meet ASHRAE 62.2 and air seal the house to prevent moisture issues, high energy bills, and air from the attic and crawlspace or basement from polluting our indoor air.  As the mantra goes, “build it tight, ventilate it right!”

A well-designed ventilation system brings several advantages.

  • It allows control over exactly how much fresh air is delivered and when.
  • You can adjust the amount of ventilation air if the occupancy changes (e.g. kids go off to college) or shut it down altogether while on vacation, or when windows are open.
  • It delivers a consistent amount of air year-round, no matter what the weather conditions.
  • It draws air directly from outside, so the air is guaranteed to be fresh.

The main disadvantage to mechanical ventilation is the cost to run the fan. There are many different types of systems, with widely varying costs. As the following case studies shows, this additional cost can be more than offset by the savings in reducing the uncontrolled infiltration.

Mechanical Ventilation Case Study

Consider the following single family detached home renovation project in Lancaster, Pennsylvania. Before renovation, the house had no mechanical ventilation, and much of the infiltration air came from the attic and basement, providing dirty air to the house. The house was leaky enough to meet ASHRAE 62.2 levels for natural ventilation. But with an infiltration rate of 1.1 air changes per hour, the house was replacing all its indoor air every hour, leading to huge heating bills.

During the renovation air sealing brought the infiltration down by 70% and mechanical ventilation was added to deliver the recommended ventilation rate, which in this case was 0.20 ACHn.

Looking at the annual utility bills, in the original house it cost almost $600 per year to heat the infiltration air. After air sealing this was cut to $217. Heating the ventilation air cost $174, and running the fan cost an additional $14 per year. Not only is the house now less drafty and more comfortable, the indoor air quality is substantially better AND the homeowner is saving $194 per year.

Not every case follows this same savings ratio. If the original house was  tighter to begin with there may not have been any theoretical savings. If the mechanical ventilation system were more efficient, there could be more savings.

But remember that mechanical ventilation puts the control in the hands of the occupant, not mother nature. If there seems to be too much ventilation, the occupant can dial it back. If there are indoor air concerns the occupant can increase the rate.

Designing an Effective Mechanical Ventilation System

There are several strategies for designing a good mechanical ventilation system, and there isn’t a one-size fits all approach for homes, multifamily buildings and commercial spaces. It’s important to keep occupants in mind and install the proper controls to make the system work for them. Everyday Green has helped MEPs and HVAC contractors select and size mechanical ventilation systems for all budgets and size buildings, homes and unit spaces. But one thing is clear: relying on air leaks to provide fresh air is no longer an effective strategy. Contact us today with your mechanical ventilation questions.

Andrea Foss

 

By Andrea Foss, Director,  Mid-Atlantic Sustainability Services

Getting it Right – HVAC System Sizing in Multifamily Buildings

Properly Sizing Mechanical Systems in Multifamily Buildings

Multifamily buildings can be a unique challenge when it comes to selecting effective heating and cooling systems. In the Washington, DC region’s mixed-humid climate, humidity control becomes a central challenge because of a couple inescapable realities.

  1. There is a lot of moisture added per square foot from cooking, bathing and even just breathing due to the dense occupancy.
  2. The small exterior envelope areas mean the air conditioner won’t kick on very often, and thus won’t have a chance to remove moisture.

High humidity can lead to complaints over comfort, condensation on registers and exposed duct work, and even mold. To effectively remove moisture, the air conditioner should run for long stretches. This means properly sizing mechanical system. Unfortunately many project teams exacerbate the problem by selecting grossly oversized cooling equipment that runs even less frequently.

Steps to Right-Sizing Mechanical Equipment

  1. Perform accurate calculations using the Manual J process to estimate peak heating and cooling loads
  2. Consult the manufacturer’s performance data at design conditions, and
  3. Select the smallest piece of equipment that will meet the load.

Common Problems When Sizing Mechanical Systems

 “Can’t I just use the worst-case orientation?”

Large windows in a corner unit can change the equipment sizing needs compared to interior units

Large windows in a corner unit can change the equipment sizing needs compared to interior units

No. In most cases the largest envelope load in apartment units is the windows. A unit with floor-to-ceiling windows facing west will have very different loads than the same unit facing north, so be sure that the load calculation reflects the actual orientation. If the same unit type occurs in more than one orientation calculate the loads for each orientation and make selections accordingly. This may require different selections and duct layouts for different orientations.

“Can I use commercial software?”

Yes, but you have to be careful. Commercial load software like Train TRACE and Carrier’s HAP are primarily geared towards non-residential space types that have very different use profiles. For instance, in an office setting you would expect lighting and equipment to be 100% on during the peak afternoon cooling hours. However, in a residential setting few if any lights are on during the day.

The commercial programs also like to include more outdoor air than you actually see in apartments. A reasonably well-sealed apartment will have very little natural outdoor air infiltration (remember only 1 or 2 sides of the apartment “box” are actually exposed to outside) and mechanical ventilation should only be about 20-35 CFM depending on the size of the unit. It is not uncommon for loads to drop by half once those inputs are corrected.

 “Will small systems have enough power to get the air to all the rooms?”

Smaller systems don't mean less power

Smaller systems don’t mean less power

Absolutely. First of all, the smallest split systems available are 1.5 tons, which is really not that small. Second of all, 1.5 tons air handlers are rated to 0.5 IWC external static pressure just like 2 and 2.5-ton systems. If that sounds like gibberish it means 1.5 ton systems have the exact same “power” to push air through long runs as larger systems.

The blower motor is smaller only because it’s pushing less air, just like a motorcycle has a smaller engine than a car but can still accelerate as quickly. We have seen 1.5 ton systems used in 1500+square feet  2-story homes. If you can’t get air to a 900 square foot apartment you have a duct sizing issue, which would be a problem no matter what size the air handler.

 “Doesn’t each room need 100 CFM of airflow for comfort?”

Well, maybe. Is 100 CFM what the load calculations show is needed? There is no such thing as a minimum airflow threshold for each room. The amount of air required is in direct proportion to that room’s heating and cooling load. If the calculations show a small load and only 40 CFM required you should supply 40 CFM. In fact, oversupplying 100 CFM will actually cause discomfort since that room will always be a few degrees off from the rest of the apartment. Sitting under an oversupplied register could be loud and drafty as well.

“But can’t I just size by bedroom count?”

No, rules of thumb don’t cut it anymore. For buildings built to 2009 or 2012 code in our climate zone (CZ4), most apartment units will have loads less than 1.5 tons, no matter how many bedrooms. There may be a few 2-ton or (rarely) 2.5-ton systems for larger apartments on the corner or top floor, but those are the exception.

If your mechanical plans show 1.5 tons for all 1 bedrooms and 2 tons for all 2 bedrooms it probably means

  1. Accurate sizing procedures were not followed, and
  2. A lot of those 2 bedrooms actually only need 1.5 ton systems

The only way to know for sure is to perform the calculations.

Conclusion

Most of these issues are the result of a very natural instinct to be conservative in the face of uncertainty. The truth is there are a lot of variables that will change the real-world heating and cooling load in a unit: how many people are in the apartment, when they are cooking, are they using blinds. The problem is in this case “conservative” means designing for temperature control at the expense of humidity control. Every extra ½ ton capacity means less dehumidification – that’s a fact. The only way to control both temperature and humidity is to perform accurate calculations, resist the urge to add extra safety factors, and size the equipment strictly according to the calculated loads.

As an added benefit, smaller equipment requires smaller electric service capacities. Especially in a rehab situation with existing service, choosing right-sized equipment is more likely to allow the use of existing service instead of requiring expensive service upgrades.