INTEGRATED BUILDING DESIGN
submitted by Alex Zimmerman

In the fall and winter of 1996-96, BC Buildings did the concept design work for a planned regional office building of about 45,000 ft2 for the BC Ministry of Transportation and Highways for Kamloops, BC.

The project used an early version of the BC Hydro Design Assistance Program process to bring a much more integrated, collaborative approach to the design process than is traditional. Teresa Coady of Bunting, Coady Architects in Vancouver acted as Design Process Facilitator to guide the team through this structured approach.

The key differences to this process was the very early discussion by all team members of all the objectives, and the use of energy analysis and costing tools to provide better quantitative information than is usually available at these stages.

The result was that, at the completion of design development stage the building design was well under the energy performance target, is within the cost performance target, and there is no exotic technology. It is the process that produced the result.

The CANMET Branch of Natural Resources Canada supported the additional design costs for this project through their C2000 program.

This article is the energy section of the Design Development report that was produced for CANMET. It describes the work undertaken by the Design Team in the Design Development phase in order to determine whether proposed design solutions would meet the performance targets for the C2000 program.

The full report is available from CANMET.

Integrated Design Approach - Process Description & Team Player Roles

DESIGN TEAM

CANMET REPORT - SECTION 4

ENERGY EFFICIENCY PLAN

a) Premises And Performance Targets

This section describes the work undertaken by the Design Team in the Design Development phase in order to determine whether proposed design solutions would meet the performance targets for the C2000 program.

The baseline for measurement for advances in energy performance is an ASHRAE/IES 90.1 Prototype building. The Prototype building specifies a level of performance based on standard orientation, aspect ratio, envelope, internal load and mechanical system characteristics.

The C2000 Program Requirements call for the design to achieve an energy performance target of less than 50% of an ASHRAE 90.1/IES Prototype building of the same area.

The ASHRAE/IES 90.1 Prototype for a building with equivalent area has a Building Energy Performance Index (BEPI) of 1004 MJ/m²*a, so 50% of that is 502 MJ/m²*a.

The performance levels that are given at the various stages represent the evolution of the design throughout those stages.

b) Computer Simulation Methodology

The primary tool that was used to simulate the building and estimate energy performance was DOE 2.1E. DOE 2.1E is an hour-by-hour simulation program that is widely used and recognized as one of the most exhaustive simulation programs available. The version used is DOE 2.1E-100, which is an enhanced version of standard DOE for additional mechanical system simulation.

The other tools used were Lumen-Micro to model the lighting system performance, LBL's Window 4.0 to model window thermal characteristics, various custom spreadsheets to complement the simulation tools. A data visualization tool called Electric Eye, running on a Silicon Graphics workstation, was used for quality assurance of the DOE runs and for some special investigations.

The basic methodology used was to perform a number of parametric runs for each of the characteristics under condsideration. The design team evaluated the results of the runs at a series of team workshops and used the results to make decisions based on the evaluation and judgment by the team members.

The simulation model was also available during the workshops in order to perform further "what-if" simulations when the design team came up with questions that had not been answered during the original series of runs.

c) General Strategies

The opportunity presented by a clean piece of paper at the start of a new design is an exciting one, but the challenge faced by any team when trying to achieve an ambitious target is, where to start? The design process was organized around a series of key investigations that proceeded from the macro to the micro issues. In order to make progress and to reduce the numbe of variables that must be dealt with at any given stage, agressive, but achievable (it was hoped) values were assumed for some key variables such as envelope, lighting, and mechanical systems.

In this way the maximum effect of any given change under consideration was examined. If this approach had not been taken, design decisions that might not have a significant effect on a conventionally designed building were given full weight. For example, changes in orientation in a building that is dominated by large internal loads may not appear to have much effect on the overall energy consumption or peak load, but in a building where these loads are reduced, the correct orientation becomes the foundation on which to build further advances.

d) ENVELOPE

Major Strategies

Three major strategies were employed in determining the optimum envelope for the building, orientation, shape and optimum fenestration.

i) Orientation

The first strategy considered was to get the orientation right. As has been detailed in Section 3.0(b), the initial reaction to the site would have suggested a form with the long axis oriented North-South. A design like that in the Kamloops climate would have resulted in a building that had significant early morning and late afternoon peak cooling loads while the useful heat gains from the sun in the winter would have been minimized. This would have increased the mechanical plant size and cost and forced the equipment to operate further down on part-load curves for more of the year, with less efficiency.

Further analysis produced a recommendation to re-draw the site boundaries slightly in order to end up with a form that had the long axis oriented East-West. This change was not modeled as the benefits were self-evident.

ii) Shape

The second strategy was to determine an optimum shape. Two forms based on the new orientation, as detailed in Section 3.0, were modeled, with 3 different areas of glazing.

The results of the modeling at this stage produced energy consumption BEPI results in MJ/m²*a as follows:

		30%	40%	50%
	Scheme 1	564	573	586
	Scheme2, N	547	558	564
	Scheme2, S	548	555	569

As can be seen, the best orientation depended on the glazing area, but most of the bent building shapes were better than the rectangle. There was not a large difference between north-facing or south-facing variations of scheme 2. The other considerations of maximising views from the building and fitting the building to the site led to the selection of scheme 2 in the south-facing variation. Although the energy performance advantage was not large, it was significant and allowed the design to maximise other design considerations.

iii) Optimum Glazing

The third major strategy involved determining the optimum amount of glazing and type of glazing. This might be better stated as determining the impact of various desired levels of glazing. The answers are not all obvious beforehand because of the number of different variables and the fact that different variables may affect heating, cooling and overall energy differently and the economics of each may be different as well. The relative impact on mechanical equipment sizes needs also to be considered.

The fundamental design challenge was to maximise the useful solar gain in the winter in order to offset purchased heat while minimising the detrimental solar gain in the summer to minimse the effect on purchased cooling energy.

In order to accurately determine what these effects were, over 100 different parametric runs were done. For each of the six building faces, a series of runs were done, varying the areas of fenestration with three different glazing types, while holding the remaining faces constant with no glazing. In this way, the incremental effect of adding a given glass type in a given amount on each face could be determined.

The three different glazing types considered were:

1. Double glazed with shading coefficient sufficient to meet ASHRAE 90.1 requirements. SC = 0.75, U = 0.65

2. Double glazed with a light tint and a low emmissivity coating on the inside surface of the outside pane SC = 0.35, U = 0.32

3. High performance glazing, typified by the proprietary VisionWall 4 layer system, SC = 0.25, U = 0.14

As it turned out, the effect for each face was linear enough that we were able to consolidate the results on one spreadsheet. It shows the effect, per face, on the overall BEPI of adding a unit area of a given glass type. see Figure 1.

Figure 1

As can be seen, the addition of any glazing increases the BEPI, but clearly the penalty is worse on some faces than others. When the effects of glazing on the heating BEPI only was examined, it was interesting to note that if glazing with sufficiently high performance was modeled, the heating BEPI per unit of glazing added is actually negative, on the two most southerly faces. In effect, the windows on those faces become solar collectors. On the next two most southerly faces, the impact is minimal. This effect has been noted before in residential design, but is rarely, if ever, seen in commercial buildings.

Figure 2

The final design solution has glazing areas expressed as percentages of total wall areas as follows:

Southwest Outside Face 22%
Northwest Face 38%
Northeast Face 38%
Southeast Outside Face 22%
Southwest Inside Face 36%
Southeast Inside Face 36%

The glazing type chosen was the medium performance of the three modeled, as givng the best performance for the best cost.

The BEPI at this stage was approximately 515 MJ/m²*a.

One other consideration came under consideration during the envelope discussions that had no additional impact on the energy but was very important in determining glazing type. The consideration here is that if the wall thermal performance as a whole is good enough, the need for under-window heating can be eliminated. BCBC has a Technical Standard that sets out minimum heating system types, depending on climate and on wall thermal performance.

In order to determine, at an early stage, whether we could take advantage of this cost-savings, a spreadsheet showing what performance levels were required for given wall systems, vs the % fenestration was developed. this gives a graphic indication of the glazing performance / mechanical system trade-off decisions inherent in high performance design.

Figure 3

Incremental Strategies

Several incremental strategies were looked at in the envelope design, namely the effect of overhangs, shading devices and trees, and variable insulation levels in the walls.

In general, overhangs and shading devices for the glazing reduced the unwanted solar gain in the cooling season and also reduced somewhat the desired solar gain in the heating season. The incremental cost of most of these devices compared to the incremental gain precluded their use on all but the top floor of the southeast and southwest inside faces.

In order to obtain the combination of shade in the cooling season and solar gain in the heating season for the lower floors, the use of deciduous trees was modeled. The height of the building and the availability of relatively large trees (in the range of 25 to 30 feet in height) for planting at the outset made this an attractive option. The consideration of suitable trees included selection of desirable species for crown shape and leaf characteristics for optimal shade in the cooling season, and minimal branch and twig cover for maximum solar gain in the heating season. Green ash was the species chosen for the southwest and southeast outside faces. Maples were chosen for the southeast and southwest inside faces.

Top floor parapets & trees reduced the cooling BEPI by 6 MJ/m²*a and increased the heating BEPI by 11 MJ/m²*a for a total increase in the overall BEPI by 5 MJ/m²*a, but because cooling is more expensive than heating , the overall energy cost is reduced. Glare is controlled and comfort increased by the addition of these features.

In general, a cavity wall that is filled with insulation contributes relatively little to the overall BEPI, especially compared to the glazed areas of the building. When looking at effects of additional insulation, that additional insulation will rarely show positive incremental energy benefits in comparison to the cost of adding it. In ths case the optimal level of insulation was determined to be R20.

e) LIGHTING AND EQUIPMENT

Major Strategies

The strategy employed to reduce the energy consumed by lighting was to increase the quality of the lighting design so that the power required by the luminaires was less than with a reduced quality design. In addition, a high quality design allows equivalent performance at reduced on-the-work-surface light levels. The light level, quality and cost were also reduced appropriate to the task in areas such as storage and circulation spaces.

Two lighting designs were considered to meet these requirements, a direct, deep-cell parabolic downlight system and an indirect lighting system.

The early design work had assumed that the lighting could be economically designed to 0.7 W/ft². Based on that assumption, the BEPI was determined to be 504 MJ/m²*a. It was recognized that further refinement of luminaire layout was necessary to determine the final lighting power density. In order to proceed to the next stage, the default assumption of 0.7 W/ft² was retained.

The final luminaire layout yielded power density levels for the indirect system of 0.79 W/ft² and 0.85 W/ft² for the direct system.

Incremental Strategies

One incremental strategy was employed to reduce lighting energy consumption, namely switching to take advantage of available daylight.

The architectural design concept from the beginning incorporated a stepped ceiling design with the ceiling heights graduated from the perimeter to the core in three steps. Daylighting inherently works better when the source comes from higher in the space. In addition to the quality improvements this offers, if the electric lights can be switched off automatically, energy reductions can be realized. This is most easily accomplished in the perimeter zone, which is 12 feet deep in this case. The amount of switching depends on the depth of the zone that is switched, the cost of the switching controls and the marginal cost of the electricity saved. When the initial lighting design has such low installed power densities, however, the incremental savings that can be economically realized are limited, particularly at BC electricity prices.

The switching strategy employed is simple step switching in the perimeter zone. The simulation model showed this to provide an incremental energy savings in the BEPI of 12 MJ/m²*a.

f) HVAC

Major Strategies

The major energy consumption challenges in any mechanical system are elimination of reheat while meeting zone loads, minimizaton of the effects of the fresh air requirements, re-use of internal heat gains to offset heat losses, minimization of transport losses, and minimization of parasitic losses in primary conversion equipment. These of course are in addition to all the normal mechanical system requirements.

The major strategy to fulfill these objectives was to select mechanical system types that best met these objectives.

Two systems were selected for study, a four-pipe fan coil system and a dual-fan dual duct system. Most of the modeling and simulation work revolved around optimising the design parameters that worked best for each system.

In the end, although the the dual fan dual duct system showed marginally better energy performance, the incremental capital cost of the system was not offset by the increased energy cost savings. The four pipe fan coil system was chosen as the system for the buildings.

The Four Pipe Fan Coil system had a BEPI of 430 MJ/m²*a while a similar Dual Fan Dual Duct system had a BEPI of 378 MJ/m²*a.

Figure 4

One counter-intuitive result of the study was that the average amount of outside air per person over the year delivered by the dual fan dual duct system compared to the four pipe fan coil was not greater than it was. The four pipe fan coil, being a "minimum air" system, was designed to deliver a constant 30 CFM per person. The expectation with the dual fan dual duct system was that, being an "all air" system, it would deliver an average outside air quantity several times that of a "minimum air" system. In the event, the dual fan dual duct system average outside air quantity was 63 CFM per person. The explanation lies in an examination of the Kamloops climate, coupled with the low internal heat gains. For economy reasons, "all air" systems revert back to minimum air quantities when the outside air is too cold or too hot to require purchased energy to heat or cool it. When the internal heat gains are low, the temperatures at which the air system reverts to minimum are closer together than they would be with a building with higher heat gains. The Kamloops climate has a much higher number of occupied hours above the temperature when the all air system switches to minimum air than would at first be supposed.

Incremental Strategies

The incremental strategies that were examined consisted primarily of optimising selections of specific euipment such as boilers and chillers to optimise efficiencies and part load operations, and optimising air and water temperature setpoints for maximum efficiency. The effect of increasing the minimum amount of outside air to increase the "free cooling" effect, as well as benefit from improved air quality, was examined.

g) FINAL ENERGY PERFORMANCE RESULTS

The last stages of the design process yielded some changes and some refinements to the design.

The area of the building changed slightly, the angle of the wings changed slightly and the final fenstration % changed. Continued work on the glazing system and mechanical system produced refinements that were incorporated in the last model.

The final energy performance for the design is shown in figure 5. At 459 MJ/m²*a, the design building shows just over a 54% reduction, which exceeds the 50% target for the C2000 program.

Figure 5

h) OTHER OBSERVATIONS

The computer simulation methodology worked well, but improvements to the process employed could be made to reduce time spent and to improve effectiveness of the workshops. While having he simulation model available during the workshops was useful, there is a limited number of runs that can be done in the workshop setting due to time pressures. In addition, quality assurance of the runs performed in the workshop setting is not as good as it can be with runs done off-line, again due to the time pressure. A better approach is to perform as many runs parametric runs as can be conceived of being necessary before the given workshop, and the results condensed, interpreted and presented for evaluation by the team.

The evolution of the design BEPI for the building over the course of the design process is also revealing. As can be seen in figure 6, progress was not steadily downwards. This reflects to some degree the iterative nature of the process. This figure does not, of course show all of the hundreds of simulations that were performed, but is a sampling if key milestones along the way. The agressive assumptions made early on about targets for given systems were not always met when the team got to those systems in detail. In the end the overall target was exceeded.

Figure 6

Some basic beliefs and notions about how an office building mechanical system performs were challenged by this design. With most contemporary office buildings the amount of solar gain and internal heat gain from electrical loads mean that the building is cooling-dominated when it comes to system design, even in a climate like that of Kamloops. In this building, the cooling loads were reduced to the point where it was clearly a heating-dominated building, both from an energy consumption and from a peak load perspective. This of course has implications for equipment selection and sizing and therefore mechanical costs.

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