Research Blog

Light Emitting Diode Coating Can Drive Down White LED Light Prices

Scientists in the US created a new light emitting diode (LED) coating from a relatively inexpensive metal organic framework (MOF) in the form of a film coating. This new alternative may be used as an alternative to existing white LED coatings, which are made of more expensive rare elements.

LED lighting has increasingly become a more attractive alternative to traditional incandescent and halogen lighting. As LED technology continues to improve to reach a more attractive price point, one of the greatest challenges involves inexpensively producing white LED lighting owners and tenants desire. Pure white LED light does not exist, and must be created from a combination of several different colors such as red, green, and blue. An alternative to using these multi-chip LEDs is for engineers to use a single blue chip. The blue chip light is then converted to white light through a yellow phosphor coating.

Phosphors used in the coatings are any substance that illuminates when exposed to light. Phosphor based LEDs are typically created from yttrium, europium, and terbium. From 2001 to 2011, the cost of these elements have risen by 400%, 600%, and 1600%, making the production of LEDs more and more expensive.

The MOF developed by the team from Rutgers University combines a common molecular chromophore, tetrakis (4-carboxyphenyl)ethylene, with zinc cations. An additional benefit of the MOF is that it can produce white light of different wavelengths by modifying the structure. The next step for the MOF is to determine how the new coating will be inserted into current manufacturing operations.


Residential HVAC Maintenance for Energy Efficiency

Proper maintenance is essential to achieving persistent energy savings with a high-efficiency HVAC system. Commonly, issues such as improper refrigerant charge, coil fouling, and clogged filters decrease a system’s performance from its rated efficiency. However, with proper maintenance, the detrimental effects of these problems can be mitigated.

The refrigerant charge in a residential air conditioning system must be set correctly to achieve desired equipment performance and life. Improper refrigerant charge can result in shortened equipment life, higher running costs due to diminished capacity causing longer runtimes, and decreased system efficiency. A study performed by Davis Energy Group, Inc found that system efficiency can be diminished by over 10% with a 20% refrigerant overcharge.

Evaporator and condenser coil fouling is also a source of diminished HVAC efficiency in residential systems. Dirt and debris clog the coils, leading to degraded heat transfer capabilities, and higher static pressure drop, causing higher fan power draw. According to a study by Ramin Faramarzi, P.E. of Southern California Edison’s Technology Test Centers, coil fouling was found to reduce system EER by as much as 35%.

Dirty air filters increase fan power consumption, because the fan must overcome the extra static pressure across the clogged filter media. Clean filters are easier for air to pass through, and thus require less fan effort to move air through the HVAC system. The department of energy cites savings of 5% – 15% just by replacing a dirty filter.

It is important to perform proper maintenance on residential HVAC systems to ensure that peak system performance is possible. Taking steps to address the problems listed here could result in energy savings of up to 35%, and will lengthen equipment life. Also, ensuring that the refrigerant charge is correct, the coils are clean and free of fouling, and that the air filter is clean will help to ensure that the rated capacity of the equipment is maintained.

Department of Energy HVAC maintenance tips for lower energy bills:

HVAC Energy Efficiency Maintenance Study by Davis Energy Group, Inc.: HVAC_EE_Maintenance_Final

Presentation with Ramin Faramarzi’s findings on HVAC maintenance technologies: HVAC Maintenance Technologies

Green Building Water Efficiency Strategies: An Analysis of LEED NC2.2 Project Data

This study analyzes project compliance paths used by a sample of projects that earned water efficiency (WE) credits under LEED for New Construction v2.2. The sample of 448 projects that earned at least one of WE credits 1, 2, and 3 indicate that credit 3 (Water Use Reduction – 90%) and credit 1 (Water Efficient landscaping – 96%) were earned much more often than credit 2 (Innovative Wastewater Technologies – 13%).

The most commonly selected option to achieve credit 1 was to have no permanent irrigation rather than reducing water consumption for irrigation by 50%. For projects that did achieve the credit by reducing potable water used for irrigation, the most common sources of reduction used were from rainwater recovery (58%) and using public non-potable sources (49%).

Rather than implementing on-site wastewater treatment (21%), most projects obtaining credit 2 did so through the water savings calculation option (79%). High efficiency toilets and urinals were the most common sources of water savings used for wastewater reduction.

Credit 3 under LEED v2.2 was earned by reducing water consumption through efficient aerators and flush fixtures to reduce water use in the building by 20% for one credit or 30% for 2 credits. Dual flush (48%) and high efficiency (37%) were the most common water closets used. High efficiency urinals (49%) were used much more frequently than waterless urinals (20%). The most common tap fittings types were:

  • Showerhead:  1.5 gpm (43%)
  • Sink – Lavatory:  0.5 gpm (78%)
  • Sink – Kitchen:  2.2 gpm (32%)



Modeling Microinverters and DC Power Optimizers in PVWatts

Solar photovoltaic (PV) module-level power electronics have become increasingly popular for residential and commercial installations. These systems have several benefits over traditional central inverters, such as:

  • Increased design flexibility
  • Monitoring of system performance as detailed as real time energy production of each panel
  • Improvement of energy capture from single panels not producing electricity rather than entire strings

One of the widest used PV modeling programs is NREL’s PVWatts calculator. This program performs simplified PV performance models based on several factors, including the array’s geographic location, orientation, and several loss factors that are user adjustable. The default losses in the software consider the case of a central inverter system and do not account for the use of microinverters or DC power optimizers. In order to model these systems, NREL has provided a set of guidelines for users to utilize to generate accurate results.

NREL identifies a set of subfactors in Version 5 of PVWatts that are affected by the use of distributed power electronics. These systems include:

  • Inverter:  Microinverters should use the California Energy Commission (CEC) weighted efficiency; DC power optimizers should include the combined (multiplied) efficiency of the central inverter and optimizer devices
  • Mismatch:  Module level power electronics are expected to eliminate all mismatch losses
  • Wiring:  Wiring losses remain relatively unchanged because microinverters will have decreased DC losses but increased AC losses
  • System Availability:  Though system availability could increase due to decreased system downtime; NREL recommends not changing this category because of potential increases in repairs for point failures in the system
  • Shading:  Some of the shading losses will be recovered and is referred to as the Shading Mitigation Factor (SMF), which represents annual percentage of shading losses recovered from distributed electronics
  • Soiling:  Soiling is generally uniform, so no changes are anticipated unless arrays have different orientations or tilts

Modeling Microinverters and DC


Measured Performance of a Low Temperature Air Source Heat Pump

A study conducted by NREL measured the performance of a 4-ton low temperature heat pump (LTHP) system over a 20 month period. The study measured parameters including system and subsystem power, various temperatures, air flow, and system status in 1-minute intervals which enabled calculation of heat production and coefficient of performance (COP) by the minute, day, and for the full heating season. The results of the study show that the technology lived up to claims by the manufacturer that the system could operate down to -30°F and supply all of the heat needed for home with very minimal use of a supplemental heat source. The data showed that the system achieved a seasonal coefficient of performance (SCOP) of approximately 2.80 over the 20 month period.

Controlling Indoor Humidity in Residential Environments

Humidity is often overlooked when it comes to providing a comfortable and healthy indoor environment. Although ASHRAE recommends maintaining relative humidity between 30% and 60%, humidity is rarely monitored in residential settings.

Excess humidity can cause a host of issues for both the building structure and the building inhabitants. High humidity can cause occupants to feel cooler during the winter or hotter during the summer, while low humidity can cause dryness and itching. High humidity can also lead to health problems by promoting the growth of mold, dust mites, and bacteria which can trigger allergic responses or asthma in building occupants. Uncontrolled humidity can also lead to condensation forming on cold surfaces which can damage building materials.

There are a number of strategies which can be utilized to properly control indoor humidity which should be considered during construction or may be installed in buildings which have humidity problems.

  • Remove indoor moisture generated by cooking, bathing, or drying clothes directly at the source and vent it directly to the exterior.
  • Ensure the building has sufficient ventilation to remove humidity generated by occupants, if the building is too tight mechanical ventilation may be required to bring fresh air indoors. Outdoor air may need to be dehumidified before being brought inside for buildings in humid climates.
  • Grade site and crawlspace to provide proper drainage. Install a vapor barrier in the crawl space to prevent moisture from entering the building from below and ensure the crawl space is properly ventilated.
  • Fix any water leaks from the building envelope or plumbing fixtures and prevent any standing water issues.
  • Install a central HVAC system which can also monitor relative humidity and provide dehumidification or provide a standalone dehumidifier.

By incorporating a combination of these strategies proper humidity control can be achieved to provide an optimum living environment to building tenants.

Ductless Mini-Split Heat Pump Comfort Evaluation

Ductless mini-split heat pumps (DMSHPs) offer an alternative to traditional central heating and cooling systems (CACs). Advantages of DMSHPs include:

  1. Reduce energy consumption
  2. Eliminate potential in-duct mold growth
  3. Eliminate duct losses
  4. Zone space conditioning

The Fraunhofer team performed field tests in two Austin, Texas homes to evaluate DMSHP comfort performance. Temperature and relative humidity (RH) data were evaluated for four spaces against ASHRAE 55 for clothing insulation (clo.) levels of 0.5 and 1.0:

  1. Living rooms:  Time percentage within comfort zones was the same for DMSHPs and CACs indicating that the DMSHP operated much like a CAC system.
  2. Bedrooms:  Residents preferred lower temperatures during the cooling season because more measured data fell within the 1.0 clo. comfort zone.
  3. Bathrooms:  Most data fell outside of the 0.5 clo. and 1.0 clo. comfort zones due to high RH levels from a lack of indoor units.

In general, measurements indicated high RH levels that suggest residents chose to achieve lower RH by cooling the spaces or were unaware of the dehumidification mode. Overall, the temperature difference observed between all rooms within each house at an outdoor temperature of 85°F was approximately 3°F.



Envelope Efficiency to Address Ice Dams

Ice dams are caused when snow packed on a roof begins to melt, runs down, and re-freezes when it reaches the roof edge (eave). If melting and refreezing persists, a barrier of ice forms at the eave which stops any meltwater from running off the roof. The meltwater then backs up behind the ice dam, penetrates under the shingles, and leaks into the building. To address the melting problem, a two-part approach is used.

The first step of the approach is to ensure adequate ventilation of the attic space within the home. Air is meant to enter the attic space through soffit vents and exit through vents higher on the roofline. This constant flow of air keeps the interior surface of the roof at a temperature consistent with outside conditions, reducing the likelihood that snow will melt off of the roofs surface while the eaves are still cold enough to refreeze the meltwater. The second step of the approach is to minimize heat transfer between the conditioned space of the home and the attic space. Any heat transfer will warm the attic space and cause the roof temperature to exceed the exterior temperature, which produces melting. To ensure minimal heat transfer to the attic space, the attic should be air sealed around all penetrations and along the perimeter to stop any hot air from rising out of the conditioned space into the attic, and the insulation levels in the attic should be consistent with current Energy Star guidelines by climate region to limit heat conduction from the interior space.

If attic insulation levels are high enough, the attic space is air sealed, and adequate ventilation is provided through the attic from the outside, the effect of ice dams should be minimized. Air sealing the attic and providing sufficient insulation levels will also reduce the heating load of the building during the winter, and the cooling load of the building in the summer. Air sealing combined with increasing attic insulation levels can see a heating and cooling energy cost reduction of 19-20% depending on climate region, according to Energy Star.


Click here to see the Energy Star estimated savings for air sealing and insulating a typical US house: