Residential integrated mechanical systems: The newest kid on the block

September 19, 2000
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The IMS concept is simple. For heating, it includes a single heat source, which provides hot water for domestic use (dhw), as well as hot water for area or space heating.

The single heat source can be an oil- or gas-fired boiler, an oil- or gas-fired combination water heater, or a hot water heat pump.

The IMS can also include a chilled-water comfort cooling system. This is modern hydronics, where the line between plumbing and hvac contracting becomes blurred.

What makes the IMS economical is new technology, such as improved insulation and efficient power burners, which has reduced standby losses and stack temperatures without increasing the risk of condensation. Combustion efficiency has been increased above 86%.

Also, anti scald valves and mixing valves are available to deliver water at selected temperatures to both the potable system and the heating system from a single hot water generator.

Controls such as outdoor temperature sensors, zone thermostats, zone valves, and zoned circulating pumps, are available to provide excellent environmental control and comfort.

How an IMS works

The prime water in the boiler or water heater is essentially sealed in a closed loop to minimize the formation of scale. The closed loop is used for space, area, and water heating.

The domestic or potable water flows through coils, or through a separate tank surrounded by and isolated from the prime water from which it absorbs heat.

Because of the lower temperature at which heat is exchanged from the prime water to the potable or domestic water, the likelihood of scale formation and thermal stress is greatly reduced. Modern heat exchange technology ensures maximum heat transfer and rapid recovery.

The controls are normally factory wired to accommodate domestic hot water priority. Manufacturers claim virtually unlimited hot water. Warranties are normally 15 years on these systems.

In the case of the hydronic or hot water heat pump, heat is absorbed from the compressed refrigerant by the prime water or the domestic hot water flowing through heat exchangers.

Also, the dhw can be stored in a separate, indirect-fired tank. Flow-through electric resistance heaters or fossil fuel water heaters or boilers are normally used to provide supplementary heat.

The most impressive new development in IMS technology is the residential combination heater. It consists of an insulated outer or prime tank, normally fired by oil or gas and an inner stainless steel tank immersed in the prime water.

The combination heater is available with a factory-mounted, fully assembled package consisting of a circulator, expansion tank, pressure-reducing fill valve, and a three-way zone valve wired for domestic hot water priority.

Older technology is based on a boiler with an external dhw tank, which contains an inner tank or heat transfer coils surrounded by prime water from a boiler. The prime water is circulated on call from a thermostat on the dhw tank.

In almost all systems, the dhw has priority on the heat from the boiler — no surprises while taking a shower.

Heat distribution for area, space heating

Hydronic space heating in homes with existing ductwork usually involves circulating the prime water through a hydro coil mounted upstream of the blower or atop a blower cabinet.

Additional prime water-circulating loops can provide radiant space heating and use tubing, baseboard or valance heat exchangers, or area heating (such as snow melting or pool heating). Modern PEX tubing or CPVC is cost effective when compared to metal tubing or pipe.

Radiant floor heating generally consists of flexible tubing mounted below the floor, through which the prime water is circulated at a relatively low temperature. This same system is also used for area heating to remove ice or snow and for heating pools and spas.

Baseboard radiation and wall-mounted convectors are also used for space heating. Prime water temperatures are usually higher for these applications than in under-floor tubing applications. Fancoils are also used where tempered fresh air is introduced to the space.

Valance radiant heating is installed close to the ceiling and generally on an outside wall. The manufacturer claims that the radiant heat is not blocked by furniture and is evenly distributed without noticeable drafts.

It has another advantage in that chilled water can be circulated for near-draftless convection cooling. And a luxurious side benefit of hydronic heating is the hydronic towel warmer.

Cooling and the ims

A radiant floor, baseboard, or wall-mounted heating convector cannot ordinarily be used to circulate chilled water for space cooling, because of the resulting condensation of water vapor.

Where adequate ductwork exists, a chilled-water or DX coil can be used in a blower cabinet or other enclosure to provide forced-air cooling.

For other residential applications, the use of circulating chilled water for hydronic cooling is advantageous. Residential chillers are based on off-the-shelf condensing units and appropriately sized chiller packages. Only one appropriately sized chiller unit is needed to circulate water, even for a very large house.

Circulating chilled water can be used with the wall- or ceiling-mounted valance system for quiet, comfortable hydronic cooling. Temperature is controlled with sensors and quiet zone valves at each unit.

These units are self-cleansing. Condensate is collected in the unit and drained to the outside or the sewer system. Valance units can be furnished with dual coils as part of a four-pipe system, or with single coils, which can be used for heating in winter and cooling in summer.

IAQ and installation

IAQ has increased in importance with the advent of tighter buildings. Makeup air should provide for at least two air changes per hour.

Depending on the climate and occupancy, this air should be tempered and, during summer, the relative humidity reduced to about 50% to minimize sweating and increase occupant comfort.

Installation of hydronic piping and control wiring in conjunction with IMS heating and cooling has been simplified by the introduction of a UL-listed, decorative surface-mount support and cover system.

One of its chief advantages is that the piping is always accessible and yet concealed behind a decorative shield.

When used in conjunction with a valance heating and cooling system, for a new residence or retrofit, the installation is not delayed while waiting for inspection, and labor costs are minimized.

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