Mark Bomberg
1. Lessons from the last 40 years
In the immediate response to energy crisis in 1970s we had two simplified concepts, one called mass and glass and the other super-insulated house. The mass, in the first approach, was mainly in the floor and without consideration of the air redistribution, the thermal mass was not effective modifier of day and night differences. The glass let as much heat out in cloudy as it gained in sunny day resulting in a poor performance of the whole system. Today, with large high-performance windows, high air tightness and thermal insulation three times higher than in 1970’s the mass and glass could function well, providing that one uses an adaptable indoor climate and has a good mechanical air handling system.
Yet, in 1970s the super-insulated house, as shown in Figure 1 was the only real proposition.
Figure 1: Saskatchewan conservation house© was a first in world, demonstration passive house built in 1978 that involved a super-insulation, solar orientation, airtightness, solar panels a heat recovery ventilator on the exhaust air.
One may ask the question why this technology did not get wide-spread applications? The answer is quite surprising – indeed it was to gainmarket but with a twist. This house was too expensive for the market, so builders decided to use the superinsulation with a trade-off, namely eliminate heating of the ventilation air and use electric heating in rooms. In effect of elimination of the chimneys, the air flows in house were modified, resulting in winter condensation on the second floor, wet attics, and a sick building syndrome when air supply was reduced.
The North American generation that grew up with the pre-conditioned air and mechanical air conditioning took the air quality for granted. Yet, spoiling the indoor air quality meant the end of the superinsulation concept in the marketplace. This is why on our website we placed a series of BSI to ensure an understanding that a good environmental control cannot be divided. When you change heat flows, you must change moisture control, ventilation and air circulation pattern. It took us one generation to learn the basic building physics. Building science was built in steps, but now it a a science of integration. Today, there is no separation between passive and geo-solar measures in energy management. To make sure that all points are considered in the initial stage of building design we created IDP (integrated design process), often called a “design charrette”, because only a few English-speaking architects remember that charrette was the carriage used to carry prisoners to the guillotine in the time of the French revolution.
Thus, we made a first step in the direction of building sustainable residential houses. Yet, this progress did not reach the field of retrofitting where the archaic concept of looking at a single function of the building system and applying simple payback is still the prevailing rule. Therefore, in this BSI closing our introductory series, is focused on retrofitting of residential buildings.
2. What is needed to accelerate energy conservation
We are slowly coming to the end of a SARS-CoV2 pandemic era that makes all of us poorer than before. Yet, the imperative to reduce the green gas emission from housing is higher and the national need for deep retrofitting follows right after the vaccination campaign.
After evaluating many different ideas, one may propose a series of amendments to both new construction and retrofitting concepts. Both new construction and retrofitting projects should be divided into two stages to solve the conflict between the limited investment funds and the society demands for reduction of the carbon emissions. Stage one is unchanged. Stage two must be designed jointly with the first stage one but the construction will be started sometime later. More specifically we propose:
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All residential buildings should be operated under an adaptable indoor climate as only the transient indoor environment enables thermal mass to contribute to energy efficiency.
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In all buildings except very small houses, should use control systems to operation of heating, cooling, illumination and ventilation.
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All improvements of heating/ cooling and ventilation systems during the post-construction requires a full year of monitoring because summer and other conditions require different setting of building automatics.
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We use as the example, an Energy Quality Management (EQM), or thermo-active building energy management system but themethodology is applicable to other systems.
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One may either calibrate one of the existing energy models or consider use of an individual monitoring and performance characterization model of energy and indoor environment. Yet the latter category of models are only now being developed and th3erefore they must be evaluated under field conditions before wide spread use.
The role of automatic controls for dynamic facades was discussed by Selkowitz in 2008 (see, white paper, 2008). This implies that windows with a high R-value and a moderate solar heat gain coefficient (SHGC) should be used in cold climates. In hot climates, the energy flows are dominated by solar gain which is highly variable depending upon climate, latitude, season, and orientation, and needs vary – i.e., cooling load controls vs daylight admittance and view vs glare control. Thus, in hot climates as well as in mixed climates, static control needs to be replaced by dynamic control of solar gain. This approach should drive design strategies and technology for the near term. In the more distant future, windows should become even greater net energy suppliers by becoming more fully integrated with photovoltaic capabilities.”
Now is the time to switch both opaque and transparent parts of the building enclosure to dynamic operation. The improvement in film photovoltaics has a great potential to increase the functions of both components of the facades. In this context, a small step that may create a scientific revolution, is to treat the existing buildings not as the energy problem but as the energy solution. This is an obvious conclusion for the Southern US states, yet calculations show that even in NY state, shallow geothermal storage integrated with water-sourced heat pump is viable.
A critical step introduced in this paper is a two-stage construction concept. It implies that there is no difference between constructing a new building or retrofitting an old one. The economic implications of two-stage construction are significant because the work is carefully planned and the investment is financially secured. This is equal is valid for the new construction as for retrofitting.
3. A new retrofitting process
Individual comfort and control of the indoor environment are the established components of the market pull, now the Covid19 experience is adding the need for variable ventilation rates and possible elimination of recycled air. Less important but still on the positive side is elimination of visible heaters or ventilators in favor of devices hidden in the construction. Finally, on the cost side we are looking for trade-offs. Concept of the Passive House in Germany won because the funds were reverted from very expensive boilers to an improved building enclosure.
3.1 Looking for the “market pull” in retrofitting
One proposes a two-stage construction pattern to both new construction and retrofitting to ensure that the second stage of construction becomes a subject to low-risk, long-term capital-based financing. As such it may generate funding for local contractors and suppliers to boost to the job market but the occupants will be able to improve their comfort and reduce the cost of home ownership and thereby the society will reduce the carbon emissions. Therefore, one will use the holistic approach and a streamlined design process.
Inclusion of building automatics significantly increases the cost of buildings so it must be seen as a necessity for integrating indoor environment with energy, as means to introduce monitoring application for performance evaluation (MAPE) that in itself leads to HVAC optimization and smart house development. The main reason for exposing the role of building automatics is the fact that it is an enabler to many small improvements and modifications that compounded will reduce the cost of the building system.
3.2 Relation between the cost and value
Figure 2 shows that a good design may initially reduce utility bills without increasing the cost and that some passive measures may create a small increase in the cost(Klingenberg et al. 2016). With a larger use of passive measures, the ownership cost (mortgage plus utilities) goes through a minimum and continue to grow. There is another characteristic point on the curve shown in Figure 2, namely a point of equilibrium in which the cost using the passive measures is the same as photovoltaic (PV) energy. One may switch to PV sources of energy and continue until reaching zero energy. This happens at a substantial investment, typically about 50 – 70% increase of the minimum mortgage cost. Yet, the unpublished experience from the Building America program indicates that a typical investor accepts up to 10 percent increase over the reference cost.
Thus, the rational design of low energy buildings requires a proper selection of the reference buildings. In line with this need, the American Photovoltaic Institute selected reference buildings based on the ASHRAE / DOE climate zones (Wright and Klingenberg, 2015) and considered 115 locations for cost optimization that included air tightness, window upgrades with a 15°C minimum interior surface temperature, heating and cooling demands, and peak heating and cooling loads. Statistical models were used to generate target properties for any location from parameters such as degree-days and design temperatures. In this way, the passive houses moved American housing one step closer to the goal of sustainable development.
Figure 2. Costs of utilities (green) and mortgage (blue) versus energy savings from zero savings to 100% savings. Point 1 is the starting point, point 2 the energy conservation measures alone, and point 3 the beginning of PV contribution (Wright & Klingenberg 2016) with permission).
Figure 2 shows that a typical investment based on the money return at a prescribed time, stops far below the zero-energy building. To alleviate this difference, one proposes a two-stage construction process. In the first stage one achieves performance level possible for the selected cost, while the second stage continues to optimize the cost for the Near Zero or Zero Energy building. In the first stage the building is completed at a low performance level (acceptable to the building code and the investor), while the designer proposed also continuation to zero energy level. The second stage starts a few years later.
The second stage of the new construction project will be subject to the same financial restrictions as a retrofitting project. Nevertheless, the stage two of any construction or retrofitting project has the advantage of known property value and an estimated cost of the new construction or repairs. This information is invaluable for a capital-secured investment.
3.3 Rehabilitation of buildings in stages
As the two-stage solution is also suitable for retrofitting of existing buildings, one can see below. Atelier Rosemont (2O16) in Montreal, Canada is a cluster of buildings designed for retrofitting that spanned a period of 10 years. Using year 2008 as zero energy reduction one arrived to 92 % cumulative reduction in 2018, with the following steps:
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High Performance enclosures; a common water loop; solar walls provided 36% reduction
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Gray water power - the cumulative energy reduction grows to 42 %
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Heat pump heating - all passive measures resulted in 60% reduction
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Domestic Hot Water with evacuated solar panels to achieve 74%
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Photovoltaic panels reduce external energy to arrive at 92% cumulative reduction.
The Atelier Rosemount cluster included a mix of different types of dwellings including social dwellings. This project highlights that modern thinking in construction eliminates the boundary between new construction and retrofitting of old buildings. Over the ten-year period, the building energy use in Atelier Rosemount fell to 8 % of the initial level. It also shows that the two-stage approach with dynamic operation of buildings as proposed in the EQM technology can become a reality including the proposed integration in time and space (Romanska-Zapala et al, 2018; Yarbrough et al 2018).
3.4 Generalization of the approach to zero energy ready design
Forty years ago, average yearly energy use in new residential buildings in North America was 200 – 300 kWh/(m2∙yr), today it is about half of it (Wallburger et al 2010) and advanced buildings use about a quarter of the previous number. The value of 70 kWh/(m2∙yr) is commonly used as the upper limit for low energy buildings. In this process, the merger of solar, geothermal and passive measures became unquestionable. Of course, the significance of solar and geothermal contributions are different between cold and warm climates, but the principles are the same.
As the total energy use depends on factors such as micro climate surrounding a building, building type and size, number of occupants and on the degree of technological development of the society, one should refrain from use of percentages or steady state descriptors like U-value. The only criterion to define energy performance is the average annual energy use per unit of the floor area. This can be established either with or without consideration of the electrical devices used by occupants and used to characterize a trend or to compare cases. Furthermore, one prefers using electrical energy instead of the primary energy. This simplification is justified by the goal to decarbonize construction as well as use of the heat pump technology, where the favorable coefficient of performance compensates the difference in efficiency of electricity production and transfer.
Energy design after including all passive measures in the step 1, follows to the step 2 and includes all low exergy measures, e.g., thermal energy storage, solar thermal panels, convective cooling, and finally in the step 3 includes other renewable energy sources, e.g., photovoltaic, thermal energy redistribution, electrical storage). When including an economic analysis, the environmental design will include four stages.
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All passive energy measures and factors affecting indoor environment such as temperature, indoor air quality, acoustics, daylight, illumination, hot and sewer water management, aesthetics and building resilience in disaster situations are addressed.
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Designed in parallel, abuilding automatic control system will integrate heating, cooling, ventilation, and other indoor climate controls including use of geothermal and solar means for energy generation and storage.
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The economic analysis performed in parallel to the technical one, will determine the level of investment for the initial stage of retrofitting. More specifically, one must decide to what extent should photovoltaics should be included in stage one of the retrofitting process?
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At end, one documents the design and cost estimate for stage 2 of the retrofitting and develops a comprehensive operational manual for the building.
In the above text, there are two differences from the current practice, namely:
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Including building automatics in the IDP team, and discussing a post-occupancy HVAC optimization that requires either verification of existing energy model or performing monitoring of the field performance and develop a specific model of energy performance
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Establishing a building manual as one requested in the contract documents. While every car is sold with the operational manual, so should with an operational manual be expected with any low energy building.
3.5 Using adaptable indoor climate.
The main reason for the reduction of the climate impact of buildings is the fact the proposed design is based on adaptable comfort (De Deer, 2018]). Hancock and Warm, proposed the extended-U model, called a Maximal Adaptability Model that discuss relatively stable broad range and rapidly deteriorates at the boundaries of thermal acceptability as illustrated in Figure 3.
Figure 3. Relation between stress and adaptable comfort zone (from De Doer and Zhang, 2018).
Over the whole optimal range of the indoor temperature the relative performance does not fall less than 4 percent. Effectively, if the temperature changes slowly e.g., 1 oC during 1-hour period, occupant do not feel any discomfort. As standards in Europe and North America permit using adaptable climate, the only reason for keeping a constant indoor temperature can be a tradition. Seventy years ago, a thermostat relied on a contact between platinum wire and mercury. Later people tried to vary thermostat setting to find that what they saved on switching one way, they lost on switching back, because they modified only one factor in an inert passive system.
Adaptable comfort was used in the Tokyo’s application of EQM technology (termed as thermo-active, Kosuke, 2020) and is beneficial in all climates with a large difference between temperature during day and night. It is also needed when an increased effect of thermal mass (or other means of energy storage) is used for interaction of the building with smart electrical grid.
3.6 Understanding air flows in the building
The second critical aspect of the proposed design relates to understanding of air flows in buildings. This part of building science is probably one most neglected area in the construction practice and not much progress was made since 1990’s when the interstitial airfield was defined (Lstiburek et al, 2000, 2002). As long as ventilation was roughly constant one could measure flows and adjust some valves connecting air ducts, but with recent progress in variable ventilation rate in is a need to quantify air flows more precisely and this becomes an important area for research needed for dynamic operation of buildings.
It is easier to control dynamic air flows if an over-pressure of air is used. But to do so, there is a need to control the moisture balance in materials. Furthermore, to perform interior retrofit it is often necessary to dry existing walls or even roofs and the whole new technology of ventilated air cavities with or without capillary active layers is this second necessary area of future research.
The lessons from Covid19 are clear. In traditional mechanical ventilation systems only part of the air is removed, and the incoming fresh air is mixed with the returned air in an air handling unit. We talk about air dilution because the whole volume of indoor air is removed in a period of 2 or 3 hours. Even in the carefully controlled ventilation, e.g., in the cabin of the airplane, a natural convective heat of passengers powers an internal loop mixing the old and fresh air. Effectively, when we talk about reducing ventilation to the level need for breathing, i.e., air exchange rate 0.33 ach it means that the whole volume is air is removed in 3-hour period, we assume that there are no stagnate zones of air i.e., a perfect mixing in all spaces. This is a minimum of ventilation for a cold day of winter. Yet, in spring or fall when we have excess thermal energy stored in the walls or furniture, we have no problem with three times higher ventilation rate and if someone is with flue, we need to have a full air exchange in ½ hour i.e., have 600 % of the minimum.
Design of such a ventilation requires to know its effect on energy and vice versa, e.g., how much can one increase ventilation to limit the room temperature change to one-degree K (two- degrees F) per hour. Furthermore, one could benefit from using the so called DOAS (direct outdoor air supply) technology. Adding exhaust ventilation on demand is optional. It can be installed in solar exposed rooms with large area of windows and provided with a manual or automatic operated exhaust ventilator. An automatic function of the ventilation system is used during the nighttime to clean the whole dwelling (and to reset it to a reference temperature if an adaptable climate control system is used).
3.7 Increasing interior thermal mass in the building
Adaptable comfort was used in the Tokyo’s application of EQM technology (Kosuke et al, 2020) and is critical to all climates having large difference between temperature during day and night. It is also critical if an increased effect of thermal mass (or other means of energy storage) is used for interaction of the building with smart electrical grid. The Tokyo application uses concrete as it has the thermal mass and physical properties suitable for mechanical loads in Japan, yet concrete exterior walls are not likely to be found in our buildings. This forces us to consider what would be the best modeling capability for a distributed mass.
There are two possible approaches in modeling: (a) simultaneous simulation (co-simulation) of two differential equations models or (b) monitoring and ANN-based performance model. Speaking about approach (a), some work showed co-simulation of Energy+ and Contam (Heibati et al, 2019) give results different from running these models separately but does not improve precision of these models. Conversely, using a modular statistical package and ANN model (Dudzik et alm 2020) appears to give much lower uncertainty. Yet, considering that ANN model is capable of addressing the real occupancy and climate factors measured under field conditions, we decided to share it with other researchers. As Confucius said “the 3000 miles journey must be started with a first, small step”; this paper is a step on the path to building automatic controls to provide a dynamic operation of buildings that are based on the adaptable indoor climate and upon these conditions the type (b) model is a winner.
4. Closure
This is not a research paper but a short note to enable an insight into the coming soon a major change in the field of retrofitting. With growing pauperization of the North American population on one side and increasing pressure on reducing green gas emission the secure place for investment are job creating technologies such as retrofitting and therefore our prediction is secure, the only question is how quickly the market will accept the change of the thinking paradigm.
Reference
Atelier Rosemount, 2016, Canada Mortgage and Housing Corporation, Newsletter, 2016
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Dudzik M, A. Romanska-Zapala and M. Bomberg, 2020,
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