Equipment for Electric Hydronic Systems
DESIGN AND OPERATION
Electric hot water or hydronic systems deliver heat to a house by means
of hot water. The three main components of such a system are:
1.
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a boiler to heat the water;
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2.
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heating equipment – generally baseboard heaters or
radiators – in most rooms, often installed against an outside wall;
and
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3.
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a pump to circulate water from the boiler to the
radiators and ensure that it flows back through the
pipes.
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Figure 5: Central boiler for an electric
hydronic system
The boiler in an electric hot water heating system is compact. Its
heating elements are immersed directly in the water (as in an electric
kettle). Where space is limited, the boiler can be installed on a basement
wall, in a closet, under a kitchen cabinet–it can even be hung from
basement ceiling joists.
If you are replacing a boiler in an existing hydronic system with a new
electric boiler, you can probably use the existing heat distribution
pipes.
MAXIMIZING EFFECTIVENESS OF HYDRONIC SYSTEMS
As with forced-air furnaces, there are several ways to improve the
performance of hydronic heating systems.
Improving Heat Distribution
Old-fashioned gravity systems that circulate the water by natural
convection are much less efficient than systems that use pumps. Slow hot
water circulation causes home temperatures to fluctuate noticeably, and it
takes a long time to restore temperatures after a night-time setback.
Also, a gravity system cannot circulate hot water to radiators or
baseboard heaters in basement living areas, where they would be below the
level of the boiler. All of these problems can be overcome by adding a
circulating pump, and replacing the open expansion tank in the attic with
a sealed and pressurized expansion tank near the boiler. If you have a
gravity system, consult your heating and plumbing contractor about the
possibility of improving it.
Balancing the Heat
Balancing the heat delivered to different areas of the house is as
important with hydronic heating as it is with a forced-air system.
Radiators are often fitted with simple manual valves that can be used to
control the amount of water flowing through them. Such valves can be used
to vary the heat delivered to different rooms in the same way that
balancing dampers are used in a forced-air system.
One device that can vary the heat output automatically is a
thermostatic valve (Figure 6) that can be set to control
the temperature in any room. However, this will not work on radiators or
baseboard heaters installed on what is called a "series loop" system. In a
"series loop", the water must pass through all the heating units on its
way back to the boiler. If there is more than one loop in the system, some
balancing of the heat output can be achieved by adjusting the valves that
control the water flow through each loop. The same type of baseboard
radiators are equipped with built-in air dampers which allow heat output
to be regulated to some extent.
Figure 6: Thermostatic radiator
valve
Conventional hydronic systems usually have the boiler temperature set
at 82oC (180oF). It is possible to reduce energy
consumption in a number of hydronic systems by means of a regulator valve
that causes the temperature of the water circulating in the system to vary
in relation to the temperature outside. As it becomes warmer outside, the
temperature of the water is reduced.
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Automatic Setback Thermostat
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| The easiest way to save heating dollars is to lower the
temperature setting of your home, when possible. An automatic
setback thermostat will adjust your home's temperature
automatically. These thermostats have a mechanical or electronic
timer that allows you to preset household temperatures for specific
periods of the day and night. As a general rule, you will save two
per cent on your heating bill for every 1oC you turn down
the thermostat at night. |
| The thermostat can be programmed to reduce the temperature an
hour before you go to bed and to raise it again before you get up in
the morning. You could also reduce the temperature during the day
when the house is unoccupied, and raise it shortly before you
return. For example, you could have the temperature set at
17oC (63oF) when you are sleeping or not at
home, and at 20oC (68oF) when you are awake.
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| Experiment with the unit until you find the most comfortable and
economical routine for you and your family. |
If you have a hydronic system, you can also reduce energy usage
through zone control. With this system, thermostat-controlled valves
on each radiator permit the control of individual room temperatures.
A heating and plumbing contractor can provide more information about
zone control and can install all the required equipment when the
heating system is installed. Zone controls are also available for
forced-air systems, usually with dampers in main heating ducts
controlled by separate thermostats located in various parts of the
house.
NOTE: For all-electric heat pump systems, setback
thermostats are generally not recommended. |
| Improved thermostats
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| Greatly improved electronic thermostats are now available on the
market. They are very sensitive and help reduce temperature
fluctuations to less than 0.5-1Co, whereas fluctuations
usually range on an average from 1.5-2 Co. They ensure
that the furnace or electric baseboard heater starts up as close as
possible to the set temperatures. The energy savings generated by
these devices vary according to the model. |
One model used with baseboard electric heaters will switch the
heater on and off to maintain ambient temperature within +/- 0.5°C
of the set point. It could save around 3% on energy use while
improving comfort considerably. This model, however, is not
recommended for fuel fired furnaces or wherever short cycling is not
desirable.
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Source: Energy Resources Canada (NRCan) -
Office of Energy Efficiency
