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Tag: Existing Building Performance

Mandatory Energy Benchmarking.. Coming to a City Near You?

Measurement enables Management; Transparency enables Accountability… The quintessential concepts driving adaptation of mandatory energy benchmarking legislation.

Commercial_Benchmarking_Policy_Matrix (cities) - 8.1.14 (2)

Mandatory energy benchmarking represents a pivotal step towards reforming energy usage in American cities, as it galvanizes populations through collective reduction. Like any immature “innovation”, the practice faces barriers and static hindering widespread adaptation and dissemination into the mainstream.

What factors influence proliferation?

Unique building stock and varied regulatory needs necessitate city-specific reporting plans. Until there is a scaleable model of best-practices, development will continue to be resource and time intensive for administration.

Complexity in execution threatens data integrity and program usefulness. Unintentional errors, difficulty in obtaining information, and unfamiliarity with ENERGY STAR’s Portfolio Manager all weaken database strength. The remedy lies in educating elected reporters. Program handlers must be well versed with the operations and techniques necessary to perform their role effectively.

Stakeholder push-back during implementation deters participation and damages program reputation. Greater visibility of post-retrofit results will dispel doubts of program usefulness, while increased availability of financial incentives will quiet claims of marginalization [under-performers stigmatized as poor living options] and unfair penalization [fining of historic buildings or financially underserved properties].

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

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.

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.