Without question, the “green tsunami” has hit our shores.
The “wave” I’m referring to, of course, isn’t a rogue monster from the deep, yet it is in response to the seismic shift in the building industry happening on a global scale. And though we Americans now embrace the need for change, conceptually, we’ve only just begun to shape it substantively.
Though in the opinion of many Asians and Europeans-with a twinge of annoyance at our weary pace-we’ve resisted the need to develop and support green technology far too long. Renewable energy development has just begun to supplant our voracious thirst for fossil fuel.
If there’s a silver lining to our current economic woes-fueled by increasing energy costs-it’s the wake-up call we received, encouraging a serious look at how we handle the need to move toward greater energy efficiency on a broad scale.
Renewable energy sources are now being developed at a greater pace than was anticipated just a few years ago. Related to geothermal is one of the fastest growing trends in the commercial building industry: the use of water source heat pumps for heating and cooling.
“Water-loop technology has been around for decades, though now-pushed by rising energy costs, the ‘call to arms’ by the USGBC, the advantages of LEED certification and substantial government incentives-interest in the technology is gaining rapidly,” said John Bailey, vice president of sales and marketing for Oklahoma City-based ClimateMaster Inc. “We refer to the water-loop process as ‘thermal energy transfer.'”
Caption: This image shows one of the “ends” of the thermal energy transfer equation: the cooling tower. Here, a technician performs routine maintenance on a cooling tower.
600% efficiency + 3-year paybacks
The newest generation of water source heat pump heating and cooling technology for large buildings has pushed operational efficiencies into the 500 to 600 percent range. That is: for every unit of energy used to operate the equipment, the system delivers five to six units of energy in return.
That’s smart use of energy. Add new and sophisticated controls to the picture, system integration with building automation systems, and supplemental energy sources like photovoltaics and wind, and you begin to see the potential for how quickly the commercial building market is evolving.
Water-source heat pumps move heat very efficiently. The best models will extract 5 kWh of heat from the water loop for every 1 kWh of electricity used to power the compressor and fan, delivering all 6 kWh as heat into the air. This 6 to 1 ratio is called the COP
(Coefficient of Performance), and can be equated to a 600 percent efficiency level.
With the potential for of-the-charts efficiency performance, building owners are now at attention. When the design engineer can calculate a three- to four-year payback for new equipment (or perhaps even shorter than that in some instances), there’s real incentive to install new technology-many of the systems are ideal not only for new construction, but also for retrofit application.
“The industry’s changing,” added Bailey. “And the market for this new technology is growing quickly. The technology continues to improve steadily and yet a large number of building owners still haven’t heard the news.”
Caption: Horwitz/NSI engineers Jeff Rusinko and Josh Counihan
(above), and Robbie Skantz (service tech, below) reviewing specs and lubricating bearings on a large pump motor.
Thermal energy transfer
Water-source heat pump, or thermal energy transfer (TET) systems provide highly efficient zone-controlled heating and cooling throughout a building by circulating water in a closed piping loop to move and exchange thermal energy. With such technology a building has, within it, many separate heat pumps, connected by closed-system water loops that transfer thermal energy with great efficiency.
Compared to traditional two-pipe, central chiller-based building systems, the installation of water-sourced equipment often saves 10 to 15 percent in the initial cost or up to 20 to 30 percent of the installed cost when compared to a four-pipe system. A high efficiency chiller is typically 10 to 15 percent less efficient than a water source heat pump (TET) system, operationally, while a standard chiller performs 30 to 50 percent less efficiently. Maintenance costs are often 10 percent higher with chiller-based systems. Heat pump life expectancy is about 20 years; a chiller will typically serve for 20 to 25 years. And, with a thermal energy transfer system, maintenance needs are also typically low.
Individual heat pumps add or remove heat from the air within each zone as required to meet its unique heating or cooling load. During zone heating, they extract needed heat (thermal energy) from the common water loop. During zone cooling, heat is rejected into the water loop where it can then be shared with all other heat pumps throughout the building. It’s in this way that rejected heat-which is wasted to the outdoors in most HVAC systems-is fully utilized before any new energy source is used to heat or cool the building.
Bailey explained that all buildings contain year-round sources of thermal energy, or internal heat gains, that are recovered and recycled by a thermal energy transfer system, such as lighting
(typically 11 to 13 Watts per square meter), people (we emit 300 to 500 Btus per hour), equipment (computers, printers, copiers, pumps and motors) and solar gain: perimeter zones may require daytime cooling even during cold weather.
The cast-off thermal energy within the building envelope recovered in the water loop of a water-source heat pump system can be used for most purposes that require heat, such as:
Space heating – Water-source heat pumps in zones that require heating will extract thermal energy from the water loop.
Water heating – Water-to-water heat pumps can be equipped to extract thermal energy from the water loop to heat domestic hot water, swimming pools and spas, or to serve hydronic loads such as radiant heat or snow-melt systems.
Ventilation – Dedicated “outside air” heat pumps extract thermal energy from the water loop to heat outside air used for ventilation.
The heat “pumping” concept
Water-source heat pumps use a simple vapor compression refrigerant circuit to efficiently provide zone heating or cooling. During the cooling mode, heat is extracted from the air and rejected into the water loop. During heating mode, the process is reversed, with heat being extracted from the water loop and rejected into the air. Thus, thermal energy is transferred, or “pumped” between the air and the water loop, in either direction, on demand.
Caption: One of many ClimateMaster water-sourced heat pumps in a LEED condo in Washington, D.C. Some were located in mechanical closets, other vertical-stack heat pump units were located within the living space.
Why water?
In a word: efficiency. Water is the most efficient way to move thermal energy.
A 2-inch water pipe can carry the same amount of cooling as a 24-inch air duct, requiring up to 90 percent less transport energy in the process and taking up far less space. The mass of the water loop also provides thermal storage, allowing a substantial amount of heat to be carried from occupied periods into morning warm-up. The advantage of thermal storage is not a capability found with traditional HVAC systems.
Water-source heat pump heat exchangers are both compact and efficient. This is because of the high mass and thermal conductivity of water. Water-source heat pumps-unlike traditional HVAC systems that are inefficiently tied to outdoor dry bulb temperatures-operate at lower condensing temperatures because they are linked to the outdoor wet bulb temperature when using a cooling tower, or deep earth temperature when using a ground heat exchanger. This leads to higher efficiencies and longer service life.
Water-loop heat pump systems combine water-source heat pumps on a common piping loop with a heat rejector and boiler, which are used to maintain the circulating water temperature within a controlled range, typically from 60 F to 95 F. The most common heat rejectors are open cooling towers with isolating heat exchangers, closed-circuit evaporative coolers, or dry coolers.
Water-to-water heat pump systems also operate very efficiently under part-load conditions, such as when a small portion of the building remains occupied after hours.
A typical building has a perimeter with outside exposure that is directly affected by variable outdoor weather conditions and a core without outside exposure that is virtually unaffected by the weather.
The advantages of water-to-water systems include:
Year-’round individual control. Each zone heat pump provides individual temperature control.
Energy savings. Tenants and building owners receive heating and cooling at the highest rated levels of efficiency.
Tenant metering. The majority of the system operating cost occurs at the zone heat pumps, which can be metered at the tenant level.
Quiet operation. Modern water-source heat pumps operate with great stealth, even thought they’re often located within occupied spaces.
Low initial cost. Water-source heat pumps are factory assembled and tested, usually incorporating all zone-level controls and hydronic accessories, greatly reducing on-site labor. They use basic low-pressure duct systems and, in some configurations, no ducts at all. The water loop is uninsulated and requires only two pipes, a supply and return, and can even be designed in a single pipe configuration.
Space is maximized; retrofitting is easy. Compact, zone heat pumps can be hidden within ceilings, installed in closets, or directly mounted within the occupied space. The elimination of large central station air handlers and associated ductwork, central chiller plants, and complex four-pipe distribution systems greatly reduces mechanical space requirements.
Downtime is minimized. Unlike large central systems, failure or maintenance operations on a water-source heat pump only affect the single zone served. Redundancy is usually provided for the minimal central components of a water-loop heat pump system.
Simple control. Control can be as basic as a unit or wall-mounted thermostat for each zone heat pump. If desired, factory-mounted DDC controllers allow zone heat pumps to be directly connected to a central building management system.
Simpler to commission and maintain. The simple, straight-forward design of water-loop heat pump systems greatly reduces the commissioning process.
Recent advancements also include the use of zero ozone-depleting HFC-410A refrigerant, further enhancing the operational efficiency of water-to-water heat pumps. Some units use 100 percent outside air. Other sophisticated systems offer a dehumidification option, allowing designers even greater flexibility when meeting more stringent building requirements.
Planning to design, build or renovate in the near future? If IAQ and energy savings are important considerations, perhaps its time to consider a solution that incorporates thermal energy transfer.
John Vastyan is president of Manheim, Pa.-based Common Ground. Vastyan is a trade journalist whose work is focused on the HVAC, hydronic, plumbing and mechanical, radiant heat, geothermal, solar and broad building systems industry. For more information, visit ClimateMaster at www.climatemaster.com.
