Green retrofit

A green retrofit is any refurbishment of an existing building that aims to reduce the carbon emissions and environmental impact of the building. This includes, but is not limited to, improving the energy efficiency of the heating, air conditioning, ventilation, and other mechanical systems, increasing the quality of insulation in the building envelope, implementing sustainable energy generation, and aiming to improve occupant comfort and health.

Green retrofits have become increasingly prominent recently with their inclusion in a number of building rating systems, such as the USGBC’s LEED for Existing Buildings: Operations & Maintenance,[1] Passive House EnerPHit,[2] and Green Globes for Existing Buildings.[3] Numerous government agencies, notably the European Union (EU). The EU support and help fund green retrofits in both residential and commercial buildings, as existing buildings make up a majority of operational buildings and have been identified as a large and growing area of consideration in the fight against climate change.[4]

Overview

Most retrofits can be considered somewhat “green” because rather than constructing a new building an existing one is improved.[5] This saves a great deal of resources that would otherwise need to be used to build the structure in the first place. When the alternative is an entirely new building, any retrofit will reduce the carbon impact of that project. A green retrofit additionally considers the environmental impacts of the design decisions made, and aims to leverage each design decision to incorporate energy saving and sustainability.

Retrofitting any building inherently carries the constraints of the current building and site. In many cases this may force project teams to consider less than ideal solutions with relation to the stated project goals. For example, the orientation of a building with regard to the sun has a great impact on its energy performance, but once a building is constructed, it's generally not within the scope of a retrofit to rotate it. Budgetary constraints also often impact the energy conservation measures proposed.[6] Until recently, green retrofits have generally been considered as one-off projects for specific buildings or clients, but given the increased emphasis on improving the energy efficiency of existing building stock in the face of climate change, they are beginning to be reviewed systematically and at scale.[5][7] The main challenge this presents for governments and interested advocacy groups is that the existing building stock is characterized by different uses, with buildings located in disparate climatic areas, and with many different construction traditions and system technologies.[8] It is difficult, then, to characterize strategies for all buildings, when each building is so different from the last.

Another reason that green retrofits have recently garnered a considerable amount of research attention is government emphasis on retrofitting old building stock to address climate change. It is estimated that up to a half of building stock is always over 40 years old.[9] These buildings have significantly worse energy performance than their modern counterparts due to: design shortcomings, deterioration in mechanical system efficiency, and increase in envelope permeability. The energy use intensity of houses in the United States dropped 9% from 1985 to 2004 due simply to improvements in end use energy efficiency and code improvements.[10] Unfortunately, this is offset by the overall increase in the total number of houses. This goes to emphasize the importance of retrofitting existing building stock with relation to stated climate goals; older infrastructure performs worse.

Components of a green retrofit

Integrated design

As with any sustainable building practice, green retrofits utilize an integrated design strategy.[11] This is in opposition to the traditional waterfall design strategy, in which architects, engineers, and contractors operate independently from one another. In an integrated design strategy, these teams work together to leverage their individual areas of expertise and solve design problems while considering all aspects of the building at once. This is imperative for a green retrofit, where the design solutions are often constrained by the existing site. This could relate to the orientation and geometry of the existing building form, the size of the site, or the installation requirements of the existing and proposed mechanical systems. Because these constraints affect all aspects of building design the only way sustainable, effective, and cost-efficient solutions can be synthesized is when project teams consider all these aspects from project start.

Occupant behavior

Many sustainable building practices are passive and can be automated, like insulation or light controls. Many others depend on the behavior of the occupants of the building to realize their fully increased energy efficiency potential. An energy efficient heating system does very little good if the windows are left open midwinter. Per Ascione et al., “...the first lever of energy efficiency is a proper energy-education of users”.[12] Green retrofits can involve training building occupants in sustainable practices and installed building systems that they'll interact with, which helps ensure that any energy conservation measures used will reach their full design potential. Training can be handled by system manufacturers or the project design team.

LED bulbs are a popular and effective choice for green lighting retrofits

Lighting retrofits

One of the most common forms of a green retrofit is a full or partial lighting retrofit. In general, a lighting retrofit consists of replacing all or some of the lightbulbs in a building with newer, more efficient models.[13]

This can also include changing light fixtures, ballasts, and drivers where necessary, and may also apply to outdoor lighting solutions. In most cases, LED bulbs are the preferred choice in a green lighting retrofit because of their greatly increased efficiency compared to incandescent bulbs, but compact fluorescent and other types of bulbs like metal halides may be used as well.

Lighting retrofits are such a popular form of green retrofit because compared to other methods of improving energy efficiency, lighting retrofits are relatively straightforward to plan and execute, and the energy savings often provide a quick return on investment.[14] Most modern LED bulbs are designed to work with existing building light fixtures and rarely involve any additional work than removing and screwing in a new lightbulb. The same applies to compact fluorescent bulbs. There is very little occupant downtime associated with a lighting retrofit, as the installation is relatively quick compared to more invasive energy conservation measures.

Lighting retrofits often also consist of implementing new lighting controls like occupancy sensors, daylight sensors, and timers. In addition to more energy efficient lamps, these controls, when correctly implemented, can reduce the demand for lighting. However due to the complicated nature of lighting controls, there is debate as to whether or not they are an effective energy conserving measure. This is mainly due to the prevalence of over-optimistic energy usage reduction estimates and the difficulty in predicting the actions of human occupants.[15] They can, however, contribute to increased occupant satisfaction.[16]

HVAC retrofits

Heating, ventilation and air conditioning (HVAC) accounts for around 50% of a building’s operating energy consumption and HVAC retrofits can account for 40-70% of savings.[17][6] Reducing this consumption can provide both energy and cost savings as part of the retrofit process, and is therefore a main focus of many green retrofits, especially in colder climates where space heating accounts for over 60% of energy use.[18] The heating system, the cooling system, the air handling systems, and any humidification systems installed in the building are often considered. Part of this evaluation also includes the ductwork, if there is any, to ensure its airtightness.[19] Any leaks in ductwork will result in a loss of conditioned air commensurate with the size of the leak, and are generally addressed in a green retrofit.

A heat recovery ventilator (HRV) is recommended for a newly air sealed home as it will use the heat from the warm, moist, stale air that is being vented from the home to warm the cool, fresh, and filtered air that is entering the home. This allows for minimal heat loss while mitigating concerns of carbon monoxide poisoning, radon gas, or harmful particulates accumulating in the home.[20]

Other green HVAC retrofits can include implementing a newer, more efficient model of the same type as the existing system, such as replacing an old boiler with a more efficient one to feed a hydronic heating system. There are other times when a larger system overhaul is merited, for example changing that old boiler for a newer ground- or air source heat pump system.

A blower door test can locate leaks in a building envelope.

Building envelope retrofits

Thermal insulation and building envelope performance are key to the overall energy performance in any building.[21] Many older and existing buildings are not insulated up to current standards, let alone up to the standards recommended in many green building rating systems. The net result of this is that many of these buildings spend energy and money heating, cooling, or conditioning the air inside them, only to see it seep out through leaks in the building envelope or through poorly insulating windows.

During many green retrofits, the first step towards improving the building’s envelope is to evaluate its current shortcomings. Air-sealing is an easily accessible and cost efficient way to improve the energy efficiency of a home that is mechanically heated or cooled. Caulking can be used to fill gaps in immobile areas like window and door frames and or poorly sealed appliances while weather stripping can be used where moving parts meet like the area between the door and the doorframe or windows that can open. These drafty areas can be found by feeling for temperature differences and drafts on days when the temperature inside the house is dramatically different than the temperature outside the house or burning incense and watching how the smoke moves to detect drafts, however a more effective way to find them is to hire a professional to perform a blower door test.[22]

A blower door test is where a door with a fan and a gauge are installed into one of the doorways and the house is depressurized. The gauge can then measure the air changes per hour (ACH) which is how many times the volume of air in the house is completely replaced in one hour. This means that the draftier a house is the higher the air changes per hour will be. Coupled with a smoke pencil and an infrared scanner to identify missing insulation, a blower door test can be a powerful tool to improve the air-tightness of a home.

Window retrofits

Windows are the weakest point of insulation in a building’s envelope by far, and so contribute greatly to how thermally effective that envelope is.[23] It is because of this that windows are another common area of focus for a green retrofit. Similar to a lighting retrofit, windows are a relatively straightforward aspect of a building to retrofit, with easy to calculate payback periods. Modern, efficient windows are generally sized for existing window openings, and so can usually be installed without much additional work on the building envelope.

There are many types of windows, and their uses are as varied as the number of types there are. Most green retrofits will replace older single-pane windows with more efficient triple-paned varieties that are filled with an inert gas such as argon or krypton.[24] These windows have greater R-values (or lower U-values), so can help insulate a space far better than single-pane windows. Others use low-e coatings to control the solar heat gain coefficient. Each type of glazing has a different use that should be evaluated based on the context of the project, and with respect to the building orientation and shading.

Green roof retrofits
The Chicago City Hall retrofitted a semi-intensive green roof in 2001 [25]

Green roofs, also called ecoroofs, have a number of major benefits, including reducing storm water runoff and urban heat island effect, increasing roof insulation, improve building acoustics,[26] and providing for biodiversity.[27] It is for these reasons amongst others that the addition of a green roof is often considered for a green retrofit.

There are a number of factors to account for when considering a green roof for a green retrofit. Firstly, the type of green roof, extensive or intensive must be decided. Extensive green roofs use a thin substrate layer for the often shorter vegetation that needs less room for roots to grow. Intensive green roofs use a thicker growing substrate to accommodate larger plant species that require more room for their roots. Semi-intensive green roofs fall somewhere in between the two. Then the strength of the existing structure must be considered; many existing structures were not designed for an intensive green roof, which can carry a considerable structural load. Whether or not the existing roof needs to be stripped or re-waterproofed. Some roofs can simply be laid over with sedum mats, while others require additional work to prepare, which can come with more costs. A peaked or sloped roof does not preclude the installation of a green roofing system, but can influence the installation costs and product choices available.

In general, older buildings with lower existing insulation values benefit the most from green roof retrofits, and where there are no modifications necessary to install one, green roofs have been shown to have many benefits.[28][29]

Passive Design

Passive design is a design strategy that uses the shape and placement of the architecture and landscaping to heat, cool, light, ventilate, and sometimes provide power to the building. Often this impacts the shape of the building envelope, the orientation of the building, and the placement of the building. The shape of the building can also create microclimates in which the building is designed to trap heat or funnel breezes for warming in the winter or cooling in the summer. While these more permanent passive design elements are more often seen applied in newly built green projects, passive design can still be a consideration in green retrofits. For example, If there are windows that receive very little sunlight in the winter or a large amount of sunlight in the summer in a home, those might be candidates for being replaced first in a retrofit to reduce an undesirable amount of heat lost in the winter or gained in the summer. Using landscaping such as planting a deciduous tree in front of south facing windows to maximize solar heat gain in the winter while shading the windows in the summer is also an example of passive design.[30]

Costs, barriers, and benefits

Possible benefits of green retrofits include:

  • Improved energy security
  • Reduced air pollution
  • Reduced or greenhouse gas emissions and impact on climate change
  • Increased thermal comfort
  • Enhanced indoor air quality and occupant health
  • Generation of local jobs
  • Reduces peak electrical demand

Possible barriers to green retrofits include:

  • Initial cost and financing
  • Lack of knowledge and experience of the designers, architects, construction workers, inspectors, and financial institutions involved in the project[6]
  • Building code regulations
  • Lack of consumer interest

The scope therefore impacts of a green retrofit vary as widely as the buildings that they are implemented in. They can involve specific building systems, like the lighting, or full renovations of all non-structural components. Because of this variation, the benefits and drawbacks of a green retrofit are commensurate to the scope of the work planned. A simple lighting retrofit is straightforward to execute and relatively unobtrusive to current building occupants, but won't generally carry as much of a benefit or cost as a larger insulation retrofit. When weighing the benefits and costs of a green retrofit, like any retrofit, each of these components must be considered to summarize the project as a total.

While it is true that green retrofits have an up-front cost, the amount depends on how extensive the retrofits are.[31] Likewise, the kind of retrofit that is implemented will also impact how fast the investment is returned in savings.

Many incentive programs condition grants based on environmental performance of the project, so both environmental and economic concerns need to be considered before a project is undertaken. The economic feasibility of a green retrofit depends on the state an installed systems of the existing building, the proposed design, the energy costs of the local utility grid, and the climatic conditions of the site. The costs incurred can be further complicated by the various stakeholders involved with the project, from building owners, developers, government agencies and consultants, as well as when these costs are incurred and how they are accounted for. Any economic incentives will depend on what country or state the project is in. These incentives will differ regionally and will affect the total project feasibility. In Ireland, for example, “shallow” green retrofits have been found to be economically feasible, though “deep” retrofits are not without government grant aid to offset initial capital costs of retrofit.[32]

Green retrofits can carry many benefits such as the re-use of existing building materials. Concrete and steel have some of the highest embodied energy impacts of any building material, and can account for up to 60% of the carbon used in the construction of a building.[33][34] They are also primarily used in the structure of a building, which usually remains untouched in most retrofits. By avoiding the largest carbon impact in new building construction, green retrofits can incur great environmental benefit. At scale, the EU has found that implementing green retrofit programs comes with the benefit of “energy security, job creation, fuel poverty alleviation, health and indoor comfort”.[8]

Most types of green retrofit introduce new building materials into the space which can themselves emit harmful indoor air pollutants. The amount, type and exposure to these pollutants will depend on the material itself, what it is used for and how it is installed. Oftentimes green retrofits also call for sealing in leaks in the building envelope to prevent the escape of conditioned air, but if this is not offset by an increase in ventilation can contribute to higher concentrations of indoor air pollutants in the building.[35]

Simple steps

Homeowners can implement green retrofit solutions in the following ways:[36]

See also

References
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  37. An old gas-boiler has an energy-efficiency of 65% and a new one 93% resulting in a 30% energy reduction and consequently a 30% CO2-reduction, if installing a wood-chips or pellets boiler the savings will be increased efficiency + cheaper fuel resulting in a total saving of 40–50% and a CO2-reduction of 100% (renewable energy), if installing an efficient heat-pump the savings and the reduction will both be around 80% (100% CO2 reduction if the electricity comes from renewable energy).
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