M/E Roundtable: Energy to Spare
Volatile energy costs are making efficiency the watchword in HVAC systems design
Energy efficiency was the focus of opening remarks at this year’s American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Winter Meeting. ASHRAE officials discussed the effectiveness of the current ASHRAE Standard 90.1-1999, ‘Energy Standard for Buildings Except Low-Rise Residential Buildings,’ and the need to both simplify requirements and push for greater energy cost savings in the next published standard in 2004. For this month’s M/E Roundtable, a panel of noted mechanical engineers brings forth various energy-related trends, innovations and concerns in specifying heating, ventilating and air-conditioning (HVAC) systems.
M/E Roundtable Participants
Timothy E. Krawetz, director of mechanical engineering, Caretsky & Associates, New York City
R. Stephen Spinazzola, P.E., codirector of engineering, RTKL Associates Inc., Baltimore
David Toshio Williams, P.E., mechanical department leader, LHB Engineers & Architects, Duluth, Minn.
Scott Siddens, moderator
CONSULTING-SPECIFYING ENGINEER (CSE): What particular challenges do energy-conservation legislation and model codes and standards pose for you in your HVAC system designs?
WILLIAMS: One major challenge is providing an integrated solution to meeting energy-conservation requirements. For a while, architects that we worked with would come up to us fairly late in the design process and ask, ‘Does this building meet the energy code?’ After some resistance due to the required calculations, we have disseminated tools such as [the U.S. Department of Energy compliance software] ENVSTD and MECCheck to those that actually design the building envelope so that at least the basic building will meet the prescriptive portions of ASHRAE standard 90.1.
However, getting the team together and demonstrating compliance based on the annual energy-cost-method calculation has been difficult. Also, in our region, the model standards and codes are at odds with various state requirements and can lead to the additional question of whether meeting state requirements is enough.
SPINAZZOLA: As a design professional, I generally embrace energy-conservation legislation and model standards and codes. These allow us to have at least a starting point from which to design. Also, there is still a large market segment out there where buildings are built for a short return on investment. Minimum standards keep these types of buildings from being energy hogs. Without minimum standards, a building designed for a two- to three-year return on investment is not going to have much in the form of energy conservation.
KRAWETZ: Depending upon the type of project and whether the goal to be achieved is airside or waterside economizer designs, the space required to install is always a major concern [in meeting codes and standards], as well as first costs for installation. Payback periods are related to this as well.
Equipment and design innovations
CSE: What current alternatives and options for energy-efficient HVAC equipment do you see as especially attractive? Have you been able to incorporate such equipment into recent designs?
SPINAZZOLA: On the mechanical side, we are designing some office facilities with underfloor VAV [variable-air-volume] supply systems. This system approach has been used in Europe for several years and is now starting to take hold in the United States. On the electrical side, we are having a lot of success with indirect lighting in conjunction with daylighting and photocell-lighting control.
The use of VAV, high-efficiency motors and economizer cycles are standard. If you want to do more for your clients, you have to push the envelope.
WILLIAMS: Geothermal heat pumps, high-performance chillers, energy/heat recovery systems and nonsteam humidification top my list of attractive systems that we have been able to use. We have expanded the use of geothermal heat pumps from smaller 60-ton systems in a city hall complex up to a 600-ton system for a multipurpose building. Our chiller selection has become more critical, with an emphasis on part-load and annual performance criteria.
A majority of our commercial building projects, with larger amounts of outside air or exhaust, include energy-recovery ventilators, heat exchangers or runaround loops.
With low winter humidity-and desire to limit direct injection-steam humidification-the cost and complexity of humidification has really risen. We have designed both commercial-scale ultrasonic and pressure-atomized humidification systems for our clients as a way to reduce operating and energy costs. These systems will be evaluated after they have been in service for some time, but at this time the payback numbers look good.
KRAWETZ: We have some clients moving very aggressively in the direction of installing plate-and-frame heat exchangers as a means of taking their chillers off-line during certain times of the year. The obvious benefit is the reduction in energy consumption when operating large-capacity chillers. Once again, the major headache during design and construction is physically fitting the required piping, plate-and-frame heat exchanger, and other equipment into the most economical space within an existing plant.
CSE: What types of control systems and communications protocols are you specifying in your designs? What are clients asking for to meter and monitor power consumption of HVAC systems in commercial and retail facilities?
KRAWETZ: Clients seem to be very conscious of the benefits associated with open protocols. The control systems themselves are moving more toward DDC [direct-digital control]. In addition to the response time connected with DDC, it is a very easy interface between controlling and tracking through a personal computer for these types of systems. Particularly in New York City, everybody involved in building a facility seems to have some type of ability to watch their electrical energy-demand load, especially during the critical summer months.
SPINAZZOLA: At this point we are writing our controls specs around the BACnet protocol as a standard. Regarding the metering and monitoring of power consumption, many of our clients do very little metering. It can actually be more
profitable to base charges on connected load in lieu of doing precise tenant metering.
WILLIAMS: We are still stuck on the systems that are provided by the major temperature-control players in our market. A few attempts at LonWorks and Internet Protocol have been made, but so far it is too difficult to coordinate and implement a working system. Metering and monitoring requests have been limited to multitenant projects.
Role of life-cycle costing
CSE: How often does life-cycle cost analysis figure into design presentations for clients? What other types of tools are valuable for demonstrating the energy savings for an HVAC system design?
SPINAZZOLA: Life-cycle cost is almost always part of the equation at some level. That said, if a particular client is building for a quick turnover in the market, first cost will often be the number one decision-maker. Conversely, most government agencies that plan to stay in buildings for 20, or even 30 years, look very closely at life-cycle costs.
WILLIAMS: Only about one in 10 [of our] projects require this sort of comparison.
KRAWETZ: We are always asked to go through [a life-cycle cost] analysis when the project involves major renovations, expansions or additions. We find it very useful presenting such things as energy-consumption charts from previous projects of similar magnitude that are already in operation.
CSE: What particular concerns or problems has your firm encountered in retrofit work? Are there inexpensive options for upgrading existing HVAC equipment to bring it up to code with respect to energy efficiency, or does it usually involve extensive replacement of equipment?
WILLIAMS: The biggest concern is space above the ceiling. Either a building is not designed for ducted HVAC systems or the building load and usage has increased or changed to a level where the existing distribution space is no longer enough. Since so many of the systems are enlarged, the electrical requirements are effected and soon we are talking about a new electrical service.
I don’t think there is a magic bullet for an inexpensive retrofit. Sometimes, upgrading the air-filtration systems and components can greatly improve the IAQ [indoor-air quality] at a relatively low cost.
SPINAZZOLA: We have worked on renovation projects in 20-year-old buildings that require complete gut renovations. Conversely, we recently completed a major renovation of a 30-year-old high-rise office building for a brokerage firm that required very little upgrade to the infrastructure. You have to look at what you are starting with, and what the program requirements are for the space.
KRAWETZ: Most often, due to the age of the equipment and related facility, projects tend to involve extensive replacement.
CSE: Describe recent projects where issues of sustainability and energy efficiency have been high priorities.
SPINAZZOLA: We are completing the final phases of a large historic renovation in Washington, D.C. The project size is more than one million square feet. Sustainable design and energy efficiency for the user-a government agency-were high on the issues list.
Consequently, the design incorporates a significant amount of green design. Specifically, it includes several innovations such as indirect lighting controlled by photocell dimming, ambient and task lighting, motion detectors to turn lights off in vacant space, a high-efficiency chiller plant and a zoned energy-management system. All these design elements were accomplished within the context of a historical renovation, which put significant limitations on how and where equipment could be placed.
WILLIAMS: We used an outside energy consultant [on one project] to suggest and model energy-efficiency strategies. I don’t think cutting-edge solutions were investigated. In a design competition, the owner’s desire for a single-story solution was found to be far less energy efficient than a two-story solution. Our design won the battle by being the most sustainable. However, it lost the war by not being the selected building solution.
KRAWETZ: I was recently asked by a client to install a 1,000-ton heat exchanger in order to provide ‘free cooling’ for an existing 6,000-ton refrigeration plant. The client already had one 875-ton heat exchanger in place. The original plant was constructed in the early ’60s, and the project posed several problems. We needed to keep the plant on-line during installation and find an adequate ‘footprint’ for the plate in a location where the new piping could be connected to the existing headers-with minimum relocation of existing systems. Ultimately, we surveyed five locations, created schematics reflecting those locations and included a list of advantages and disadvantages as well as budgetary pricing.
In order to reduce the size of the heat exchanger, we based the delta-Ts of the heat exchanger on the delta-Ts found on an [existing] steam-based chiller in the plant. The increase in the condenser-water delta-T across the plate shrunk the size enough to ‘shoehorn’ it between, but offset from two existing chillers in the plant. The piping headers were virtually above the heat exchanger. There was also adequate servicing area. The only items requiring relocation were a workbench and a wall-mounted light with an associated switch.
CSE: In your opinion, what is the major issue to consider when developing energy-efficient HVAC designs today?
KRAWETZ: First costs are the primary concern.
WILLIAMS: Getting a high enough interest in energy efficiency to increase the project budgets.
SPINAZZOLA: The single most important issue is the design philosophy of the team. Energy conservation and sustainable design are a philosophy of design, not features that are plugged into a building. Before the pencil hits the paper, the team needs to know what the programmatic objectives are relating to green design.
Green design does not automatically relate to more cost. There are a lot of features that can be incorporated into a project that have a significant positive impact on the energy performance and do not cost more to add.
Cogeneration, Alternative Fuels and HVAC
The use of cogeneration for electricity and heat is having a definite impact on integrated systems design. It would seem that the owners who are most open to innovative uses of cogeneration and alternative fuels are the high-tech companies-the ones who look to cutting-edge technology in their own business operations.
‘We do a significant amount of design for high-reliability facilities: data centers and server farms,’ says Stephen Spinazzola, P.E., codirector of engineering at Baltimore-based RTKL Engineering. ‘They all have on-site generation for emergency power. With the energy crisis in California, there is now more interest on the part of our clients for on-site cogeneration … Cogeneration provides another method to provide reliable power to a facility. One key feature of cogeneration is the option for third-party turnkey plants. There are several companies that will build on-site cogeneration, own or operate the facility and sell power and chilled water to the data-center owner. This allows the data-center owner to take the financing of the power and cooling infrastructure off the books.’
Not only does the type of client have an impact on interest in cogeneration, but there are also regional considerations.
‘Only a couple of our clients have actively pursued cogeneration or alternative fuels,’ says David Williams, mechanical department leader at LHB Engineers and Architects, Duluth, Minn. ‘Our regional electrical supply is inexpensive and structured in such a way as to limit the economic incentive to install such systems. Our firm has followed the growing use of such systems and we do expect to design more of them as time goes on.’
Energy Efficiency with Standard 90.1-1999
The current version of the American Society of Heating, Refrigerating and Air-Conditioning Engineers/Illuminating Engineering Society of North America (ASHRAE/IESNA) Standard 90.1-1999, ‘Energy Standard for Buildings Except Low-Rise Residential Buildings,’ offers features that may well have an increasing impact on the HVAC-design community in the near future.
When Congress passed the Energy Policy Act of 1992, it amended the Act to require all states to update energy efficiency provisions in their building codes to meet or exceed ASHRAE/IESNA Standard 90.1-1989, ‘Energy Efficient Design of New Buildings Except Low-Rise Residential Buildings,’ and to certify within two years to the Department of Energy (DOE) that it had done so.
The legislation also required that should Standard 90.1-1989 be amended, the DOE would have to decide whether the revised standard would improve energy efficiency and require states to meet or exceed the revised standard in their codes.
The DOE plans to release the results of its comparative analyses of Standard 90.1-1989 and its revision, Standard 90.1-1999 this spring. States could very well be called upon to meet the more stringent requirements found in the 1999 standard. Moreover, the minimum equipment efficiencies prescribed in the 1999 standard will become effective after October 29, 2001. This is the date when existing equipment that was in compliance with the 1989 standard must meet or exceed the current standard.
One significant overall change in the 1999 version was that this consensus standard was reorganized and rewritten in code language to facilitate its incorporation into building codes. Also, because the standard is subject to continuous maintenance, it can be updated at any time. For this reason, it is important for HVAC-design professionals to keep informed as to changes.
Another significant change was that the scope of the 1999 edition was expanded to include both new and existing buildings and building systems.
With respect to compliance, the standard defines three options:
Prescriptive mandatory requirements.
Energy-cost budget (ECB) method. This uses both mandatory provisions and a computer methodology that allows for tradeoffs between systems and components. The ECB approach requires simulation software that can analyze energy consumption and model design.
Simplified Approach. This method streamlines the process. It consolidates information so that a user can quickly locate relevant prescriptive materials.