Maximization of space, ease of retrofit. As compact as they are, zone heat pumps can be hidden in ceilings or closets or directly mounted in occupied spaces. This, along with simple rezoning, makes water-loop-heat-pump systems well-suited for retrofit applications, particularly historic structures with limited space for mechanical rooms or mechanical chases above ceilings.

Article Tools

• 

advertisement

Minimal downtime. If a WSHP fails or requires maintenance, only the zone served by that WSHP is affected. With 100-percent redundancy typical for central components, there is little or no loss of service. A vertical-stack unit typically can be repaired, serviced, or replaced within an hour or two. A unit installed above a ceiling may require additional time, but rarely more than a couple of hours.

Simple design. With an assortment of pre-engineered configurations (see “System Configurations” sidebar), WSHPs are appropriate for various locations and loads. Additionally, with minimal controls, basic low-pressure duct, and simple piping, they can be designed faster and more cost-effectively than other HVAC systems.

Simple control. Control can be as basic as a unit- or wall-mounted thermostat for each zone heat pump, or zone heat pumps can be connected to a central building-management system via factory-mounted direct-digital controllers. The only other controls necessary are those needed to maintain water-loop temperature.

Simpler commissioning and maintenance. Many HVAC systems take months to commission properly because of complex air and hydronic balancing and/or the debugging of complicated control systems. The simple, straightforward design of TET systems greatly reduces that process. Zone heat pumps are available with direct-digital controllers, automatic water-flow control valves, and other accessories as factory-assembled and tested units. Meanwhile, basic low-pressure duct systems require minimal balancing and only basic air-conditioning service skills to maintain.

INDOOR-AIR QUALITY

ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, requires significantly larger amounts of fresh outdoor air for buildings. The challenge is how to introduce, condition, and deliver that air. Traditional options such as two- and four-pipe fan-coil systems must be upsized significantly to handle the additional conditioning load. This means larger, more expensive units and piping and larger boilers and chillers. In comparison, water-source systems take up less space and cost less to operate while introducing 100-percent outdoor air.

For past HPAC Engineering feature articles, visit www.hpac.com.

---

A journalist focusing on the plumbing-and-mechanical and radiant-heat industries, John Vastyan is the owner of Common Ground, a trade communications firm. He can be contacted at cground@ptd.net.

System Configurations

Vertical stack/high rise. Vertical-stack, or high-rise, units typically consist of a cabinet and a slide-in chassis. The cabinet includes riser piping, a blower section, controls, a drain pan, and hardware for flush-mount installation, while the chassis contains refrigeration components. Such a system can be ducted or ductless. A return-air panel completes the installation.

A vertical-stack/high-rise system offers a number of installation advantages. With piping pre-attached to the cabinet, all that a contractor has to do is connect the risers from the floor below to the floor above. Also, a cabinet can be shipped and installed ahead of a chassis to avoid on-site damage and storage issues.

Servicing a vertical-stack/high-rise unit involves minimal tenant disruption. The chassis can be removed quickly, while all electronics typically are of the “quick-connect” variety, and water connections are made via flexible stainless-steel braided hoses.

Console. Non-ducted console units are suitable for perimeter areas and for single non-partitioned zones, such as motel rooms and hospital rooms. They also are suitable for single or multiple fixed interior spaces. Furnished with a decorative cabinet, they typically are located within the room or space to be conditioned — usually, on the floor at the outside wall.

Vertical water-to-air. Space-saving vertical water-to-air units commonly are used in apartments, condominiums, and core areas of office buildings. Air is distributed through ductwork. Units can be installed where a room acts as a return-air plenum or equipped with return-air ducts. Heavy-density insulation provides acoustic absorption.

Horizontal water-to-air. Ducted horizontal water-to-air units are concealed within ceilings. They come with factory-installed hanger brackets for use with threaded rod and isolation grommets.

To minimize sound, use of a discharge duct — ideally, one attached to the return-air inlet — with at least one change of direction is recommended, as is use of acoustical ceiling tiles.

Large-tonnage horizontal and vertical water-to-air. The capacity of large-tonnage equipment typically ranges from 60,000 to 300,000 Btuh. Vertical units are designed for free-standing application in mechanical rooms and closets with ducted discharge and either ducted or non-ducted return. They are connected to closed water loops and provide either heating or cooling. Horizontal units, with capacities of up to 120,000 Btuh, typically are ceiling-hung.

Water-to-water. Water-to-water heat pumps provide either chilled or hot water while still taking advantage of heat transfer through a building's loop piping system. Typical applications include fan coils/air handlers used to pre-treat outside air, radiant floor heating, snow/ice melt, industrial-process control, and domestic-water heating (usually, with an optional plate-type heat exchanger).

Rooftop water-to-air. Rooftop water-to-air systems provide all of the benefits of packaged water-to-air systems while saving mechanical space. Typically, they are supplied with extended-range water and refrigerant circuits for both water-loop and ground-loop applications. The retrofit of a water-source rooftop unit provides a 40- to 50-percent increase in efficiency over an air-to-air system.

Dedicated outside air. Dedicated-outside-air units allow designers to incorporate an outdoor-air-treatment system into a building. Also, they provide substantial operating-cost savings and work in conjunction with space-conditioning WSHPs. Horizontal, vertical, and rooftop configurations are available in capacities of up to 100 tons. Horizontal and rooftop units also are available with an energy-recovery wheel.

Acceptable Use Policy blog comments powered by Disqus