What are They?
Utility companies will often offer their customers the ability to choose an alternative rate structure. Sometimes these are referred to as “Off-Peak” or “Time-of-Use” rates. Utilities are often subject to peak demand. That is to say at certain points in the day their customers demand more energy than at other times. This peak demand usually occurs during the day. Offices, factories, etc. are all demanding energy at the same time. The utility companies need to meet this demand.
To meet this demand, utility companies have a number of strategies. They can bring more power on-line (if they generate power themselves) or they can buy the extra capacity from the open market. The problem with this, though, is that the additional energy they produce or buy generally comes at a higher price. Yet the price they charge customers (under the normal rate tariff) is always the same.
Enter Time-of-Use Rates
However, if the utility companies can persuade their customers to shift their demand for power to a different part of the day, then this would lower the company’s peak demand. It would reduce their need to bring on-line or buy additional power at the higher rates. It can also delay the need for adding additional and expensive infrastructure – more power generating facilities, higher capacity power lines and transformers, etc. By simply shifting some of that peak demand to a different time of day the company can save all that additional investment.
What it Means to the Consumer
An “Off-Peak” or “Time-of-Use” rate has a different rate or cost for that energy depending on when that energy is used. Much like long distance phone calls, if you call later in the evening, the cost of that phone call is less. And so does a Time-Of-Use rate. The exact rate and the time at which these lower rates kick in vary from utility to utility. Often the “Off-Peak” rate is half (or better) than the Peak Rate. That can add up to significant saving on your energy bill if you can take advantage of these rates.
In a later post I will describe how you can do just that as well as how SmartRooms can really help you take a bit out of your energy bill.
In the first part of this series I described how conventional hot air heating systems lose energy through conductive heat loss. In Part 2, I’ll describe how radiant heat differs from hot air systems and how that translates into energy savings.
Radiant Heat is Different
Unlike hot air systems which use energy to heat up air, then move that air around to warm objects and people, radiant heat transfers its energy directly to objects and people. There’s no middleman. That’s why on a cool day when the sun pops out from behind a cloud you instantly feel warmer. Radiant heat warms you directly (at the speed of light) and there’s no waiting around for the air to first warm up.
Radiant heat is also very different in that the operative temperature of the system (the actual average temperature of the radiating surface) is generally significantly cooler than a hot air source. Let’s take a radiant heated floor as an example. Most radiant floor systems are set to a temperature of 70oF to 74oF. Recall that in the first part of this series, a hot air baseboard emits air at 120oF. Recall, too, that the rate of heat loss is directly affected by temperature differential – the difference in temperature between the warm side and the cold side. With an outside temperate of 0oF and hot air washing up the wall at 120oF we have a temperature differential of 120. With radiant heat we have a temperature differential of only 72oF (taking an average between 70 and 74).
Revisiting the Numbers
In the first part of this series I worked through the numbers for a hot air system. To summarize: hot air washing up an exterior wall lost 6 Btus of energy per hour through an R-20 wall and 60 Btus of energy through an R-2 window. Let’s now look at the numbers for radiant heat. The math for 1 square foot of wall is as follows: 1/20*72 = 3.6 Btu per hour. For a window it is: 1/2*72 = 36 Btu/hour.
Compare 60 Btu/h versus 36 Btu/h and you’ll see that hot air systems will lose 167% more heat through a wall or window than does radiant heat! That’s 167% more energy going out through the wall or window during the heating cycle.
Not the Whole Story
A truly astute reader will notice that once the hot air system is off (because the thermostat is eventually satisfied and thus shuts the system down) the air temperature at the wall will no longer be at 120oF but 72oF (on average). That’s very true. When the room air has reached the desired temperature, both systems will lose heat at the same rate. So one cannot simply state that hot air systems always use 167% more energy than radiant heating systems. That would be overstating it. The two systems eventually (theoretically) will equalize for a portion of the heating cycle and thus have equivalent losses. The major thing to note is that while the hot air system is on, the heat lost through the wall and window (and thus not available to heat the room) is significantly higher than that of the radiant heating system.
And that’s only one way in which radiant heat saves energy.
In subsequent posts in this series I’ll describe other ways in which radiant heat is more energy efficient than conventional hot air systems. Stay tuned!