Novitherm™ Heat Reflectors – Understanding Heat Reflectors and Heat Transfer

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1. Overview
Installing Heat Reflectors allows one to tackle the inefficiencies of your building’s hot water distribution system by reducing 90 per cent or more of the heat loss through the exterior wall immediately behind perimeter heating units. It will allow one to operate a hydronic heating system at a lower supply water temperature, and increase the comfort within the living and working environments. It is a simple and basic method of being more energy efficient, increasing comfort, saving money and reducing greenhouse gas emissions.

Typically, when people refer to hydronic (hot water) heating, not much thought is given to the processes involved in producing and distributing that heat, nor the forms of heat transfer. Usually we think of heat in terms of air temperature, and whether there is too much or not enough of it at that moment. However, when it comes to reducing heat loss, and therefore, associated heating costs, with Heat Reflectors these processes and forms should be understood.

The trend over the past 15 to 20 years has been to concentrate on improving efficiencies within a hydronic heating system at the heating source – in the boiler room. We have seen a multitude of innovations resulting in their combustion efficiencies rising from 50 or 60 per cent to over 80 per cent as a standard. In the case of "high efficiency" equipment, this figure can exceed 90 per cent.

Boiler and building control systems have evolved from simple on/off switches to that of sophisticated computer technology. No longer are they based upon a single temperature variable, but rather the monitoring of multiple points and timing functions with programs calculating optimum operating parameters to deliver the best operating efficiencies from the heating equipment.

With all the advances made in supplying improved combustion and operating efficiencies of boiler systems, not a great deal of attention has been dedicated towards the distribution (radiating) side of boiler systems. Almost all measures have been concentrating on the supply side (boiler room) of heating systems. Whether you have upgraded your boiler room efficiencies or not, it is on the distribution side of the boiler room wall, and not the boiler side, whether the heat energy put into hot water is used wisely, or wasted. Short of improved pipe insulation and some radiator valve advancements, not much has been done to increase the distribution efficiencies of hydronic systems. That is, until the introduction of the Heat Reflector.

2. Heat Reflector Operation
Installing Heat Reflectors behind radiators, and within convectors and base board heating units, will allow you to take advantage of the above laws of thermal dynamics and heat transfer. Since the emissivity of the Heat Reflector is at 0.90 or higher, it will reflect at least 90% of the radiation that strikes it. Therefore, the exterior wall immediately behind the heating unit will not be exposed to high levels of radiant energy, which is typically conducted through the exterior of the building and lost. In addition, the insulating pockets of air behind the Heat Reflectors further reduce heat losses normally due to convective and conductive processes.

Due to this reduced heat loss behind each heating unit with the Heat Reflectors installed, the heating system will retain more heat. Much of the heat normally lost through the exterior wall will now remain in the water within the distribution system. This will result in less of a drop in temperature of the system’s return water going back to the boiler room. Understandably, the greater the heat loss through the exterior wall behind the heating units, prior to the installation of the Heat Reflectors, the greater the increase in return water temperature after the Heat Reflectors are installed. The distribution system simply will not lose as much heat as it did before.

Increased return water temperature, by itself, is undesirable, unless one was initially short of heat within the building. It can lead to overheating of the heating space and a system wide decrease in efficiency. This typically results in windows opening, creating a more comfortable temperature, but also an increased heating load. A marked increase in return water temperatures with most boiler systems will cause the firing cycles of the boiler(s) to be more frequent and of shorter duration. Whereas, just the opposite is desired to increase overall system performance … longer running times with lower temperatures and with fewer cycles.

To take advantage of the increased return water temperature and receive optimum energy savings, one should reduce the building’s supply water temperature. (Control Adjustments) The effect of reflected radiation from the Heat Reflector in "cold" buildings most often causes a significant increase in comfort levels.

3. Heat Transfer
To look at how the Heat Reflector increases the distribution system efficiencies, one needs to first understand what happens to the thermal energy contained within the distribution network of pipes and radiators. Three basic means of heat transfer (transferring heat energy to the surroundings) are involved in the distribution system … conduction, convection and radiation. A fundamental certainty common to all three processes is that heat energy moves from hot to cold. The greater the heat differential, the more rapid is the energy movement.

Conduction involves the transfer of heat energy physically, molecule to molecule. A body, object or surface of a higher temperature will physically transfer heat energy to adjacent lower temperature molecules in an effort to reach a common temperature. For example: heating a pot of water on the element of an electric stove conducts heat energy from the element to the pot and the pot conducts this heat energy to the water.

Convection involves the passing of heat energy by the circulation of a liquid or a gas. For example: the water within the pot on the stove would pick up heat energy through convection currents within the water as the pot conducts heat to it. Further, the air in contact with the stove element, pot and water would pick up heat energy by convection.

Radiation involves the process of passing energy from one body, object or surface to another through some medium, typically air, which in itself is not heated. For example: the wall adjacent to the stove element is heated by radiation. The wall will typically be at a much higher temperature than that of the surrounding air.

Fundamentals of heat transfer for heating a pot of water on a stove are no different when applied to boiler water in the distribution systems of hydronic systems. Piping and heating units will conduct heat to all objects in contact with them. Piping and heating units provide heat sources for convection. Piping and heating units transmit heat energy (in a straight line) in all directions to all objects by radiation. Objects heated by radiation will conduct heat away from the source of the radiation.