ACHRNEWS

Commercial hydronic radiant floor heating

August 30, 1999
Hydronic radiant floor (HRF) heating is not a new concept. But over the last few decades, due to advances in technology, it has been rapidly growing in popularity. This growth is measured by the millions of feet of tubing sold each year in North America.

The most explosive growth has been in the custom residential building market. Homeowners and builders have come to realize the comfort and energy efficiency that HRF systems can provide, and are quite often willing to pay the higher installation costs compared to forced-air heating to obtain these benefits.

Over the past decade, most of the marketing emphasis has been put on the residential market, promoting the comfort benefits of HRF. When it comes to commercial applications and installations, the same marketing push has not been made.

The commercial area, however, is still growing in popularity as people and companies are realizing the benefits of HRF in commercial applications.

Maintaining Warmth

One of the most popular commercial applications for radiant heating is in equipment maintenance facilities in cold climates. The radiant heating systems in these facilities provide a much improved working environment, as well as a more efficient facility.

From the health and safety point of view, there are several advantages.

One of the key advantages noticed by many such facilities is the reduction in sick days taken by employees due to back or joint problems. Mechanics and maintenance personnel no longer work on equipment while lying on cold floors. Instead, the HRF system provides a comfortable surface to work on if the job requires.

During winter operations, the facility itself is much safer. When using an HRF system, there are no concerns about ice forming on the floor of the facility when a cold piece of equipment is brought in to defrost or be worked on.

Moreover, any puddles of water that form on the floor as the equipment defrosts evaporate quickly, minimizing the chance of workers slipping and falling due to a wet floor.

As for the efficiency of the facility itself during cold weather conditions, this is improved dramatically over a maintenance facility that is heated using a forced-air system. The HRF system can be designed to have enough thermal mass to defrost a specified piece of equipment in a given amount of time. This reduces the amount of time required to defrost the equipment before it can be worked on.

Also, an HRF system has a faster recovery time when large overhead doors are opening and closing, because the HRF can use its thermal mass to quickly restore the building temperature.

Working in Comfort

Another popular commercial application for radiant heating is in manufacturing and warehousing facilities. The radiant heating system provides storage and working areas that are free of obstructions since the heating system is essentially hidden in the structure of the building.

Also, these types of buildings usually incorporate high ceilings. In a high-ceiling building, stratification of heated air can cause a reduction in the efficiency of the heating system.

Radiant heating is more efficient in this instance, because a radiant system heats the objects in the building rather than the air. Radiant heating greatly reduces the inefficiencies that may be the result of stratification of heated air in the building.

Radiant heating is especially well suited for manufacturing processes that are sensitive to airborne contamination. In this type of facility, it is much easier to isolate airflows and air movement between various areas in the facility.

Also, the amount of air movement required can be reduced to the minimum required for ventilation purposes.

Commercial office buildings also gain from the use of radiant heating systems. Few people will argue the fact that a radiant heating system provides excellent comfort. Also, few people will argue the fact that a comfortable employee is (typically) a more efficient employee.

Other common commercial applications include correctional facilities, educational institutions, churches, hospitals.

There are few people who will debate whether or not HRF heating systems are more efficient than forced air heating systems. Instead, the debate has changed to exactly how much more efficient HRF is. The exact number depends primarily on the type of building.

But the key point to remember is that there are energy savings to be had. When yearly energy costs are measured in tens of thousands of dollars, a savings of a few percent results in a significant dollar value to repay the initial investment.

A Matter of Scale

When it comes to differences in the design and installation of a residential and commercial radiant heating system, the key difference is the scale of the installation. All of the basic rules still apply, regardless of the type of installation.

The maximum loop lengths allowed are determined by the size of the tubing used. The maximum flow rates through the loops remain constant.

The high-temperature boiler water must be reduced to a temperature that can be used by the HRF system. The maximum supply temperature to the system depends on the type of tubing installation and floor coverings.

If unequal loop lengths are used, balancing must be taken into consideration to ensure proper heating in all areas. The same software programs used to design a residential HRF system can be used to design commercial HRF systems.

The mechanical components used in the system will be on a larger scale. Commercial manifolds may have 20 to 30 loops compared to residential manifolds with four or five loops.

System flow rates may be measured in hundreds of gallons per minute (gpm) rather than tens of gpm. System flows may be controlled by multiple manifold pumps rather than a single system pump. Heating loads may be measured in millions of Btu rather than hundreds of thousands of Btu.

The control of a commercial HRF system does not need to be more complex than the control of a residential system. The largest difference between the two systems would be a boiler staging and rotation control.

When dealing with a commercial application, it is rare to have a single boiler in an installation. More commonly, a multiple or modular boiler system is used.

In order to achieve maximum efficiency from a multiple-boiler system, proper control is required. This would involve a control that can intelligently stage and rotate the boilers, as well as provide outdoor reset.

In order to ensure the maximum performance and comfort from the HRF system, the water temperature to the system must be accurately controlled. Accurate control of water temperature will prevent overheating, underheating, and temperature swings in the building. This means using a controllable mixing device in the system with a control that can, as a minimum, provide outdoor reset and boiler return protection.

Variable Speed

In a commercial application, the mixing device is most likely to be a three- or four-way mixing valve because of the flow rates involved. However, variable-speed injection pumping can also be used for commercial mixing.

If a control with a built-in variable-speed drive cannot provide a high enough flow rate to satisfy the system, there are two options that can be used.

The first is to use multiple controls and multiple variable-speed injection pumps and break the system into several smaller systems. Each of these smaller systems would be serviced by its own mixing control and injection pump.

The second option is to find a control that can operate an external variable-frequency drive (vfd). The vfd is then used to drive a larger pump that can meet the required flow rates for the mixing system.

It is the job of the designer to do the cost comparison between the different options, to determine which is the most economical.

Control of the air temperature in the heating zones remains the same. Either conventional thermostats or an electronic control that reads a sensor can be used.

The only major difference that may be found is when dealing with a large, open area, such as a warehouse. In this case, it is often desirable to have an average temperature for the area rather than relying on a single temperature reading.

An electronic control can be incorporated that can determine an average temperature for the area based on several sensor readings.

At the end of the day, “residential” and “commercial” are terms that we use to describe buildings with different uses. However, heat is always heat, and heat does not understand the difference between residential and commercial.

Clifford McNeill is a sales and marketing/application engineer with tekmar Control Systems Ltd., Vernon, B.C., Canada; 250-545-7749; 250-545-0650 (fax); www.tekmarcontrols. com (website).