How are Haven Hot Tubs are built differently to be energy efficient? article by- Vince (7/26/06)
Thermally Sealed vs. Full Foam Insulation Objective Comparison of Spa Energy Efficiency-Click Here on This Link
"Thermally Sealed Spas" are engineered differently than almost all of the major Hot Tub and Spa brands. Almost all major manufacturer spas are constructed with a "full foam" design. This means that the interior spaces underneath and inside the spa cabinet are filled completely with a sprayed in foam substance. Although the purpose of this dense foam is to add structural support for the shell of the spa, it has been called "full foam insulation" by the manufacturers. This 30 year old design is wide spread in use, but, it's design does not conserve electrical energy. While the foam does in fact provide insulation qualities it is not the most efficient insulation. More about "full foam"design and its limitations later.
Note the open space
under the shell. When this space is sealed up it is air
tight.A very few modern manufacturers, use a modern efficient insulation method called "thermally sealed" insulation. The concept is this. The air space underneath and on the insides of the spa cabinet are left open. This hollow air space is sealed up and made air tight with thin walled rigid insulation plus other layers of insulating materials. This leaves a closed sealed air chamber which acts as insulation very similar to an insulated thermos bottle. This sealed air chamber, also, houses the pump motors of the spa. All of the heat from the motors is captured and warms the air in the chamber below the spa. This is why "thermally sealed" designs are inherently energy efficient. This design captures motor heat and warms the spa water with it. Furthermore, any air injected into the spa via air injection or a blower pump is drawn from this warm air chamber thus further capturing the heat and warming the spa water. Want to learn more about "thermally sealed" Haven Spas? Read this!
It is a fact that, in many cases the spa heater in a thermally sealed spa rarely needs to come on to heat the water. For example, in my spa the heater does not ever come on (unless I've changed the water). The spa water is maintained at 101 to 103 degrees without using the heater. I have set the spa controller to "economy mode 1". This means the temp set point is dropped 30 degrees. The heater will not come on unless the water temp is 71 degrees. The ambient air temp and water temp here is 80+ degrees. That is how I know the heater can not come on. The spa is used daily for 90 minutes. When I remove the cover 24 hrs later the water temp is always 101 to 103 degrees....without using the heater. My costs are for the circulation pump and the jet pumps when I am actually sitting in the spa with the jets on. ***Click here to calculate the costs***
In addition, to capturing and re-using motor heat a "thermally sealed" design provides a very high insulation value. The sealed warm air insulation space provides a nearly infinite R value. As long as the heated air chamber has a temperature equal to or higher than that of the water, no heat can escape from the water below or on the sides of the spa. In cold winter climates, a thermally sealed design will will hold its heat for days thus protecting the spa plumbing and pumps from freezing days longer than a full foam design.
Why "full foam" is not energy efficient: In a full foam design all of the pumps are placed in a small box under the skirt of the spa. Heat buildup is a problem in the small equipment box. There is a vent on the side of this equipment box. If temperatures become too high in the equipment box (on a hot day for example) the system shuts off until the temp decreases. The vent is there to let the heat generated by the motors escape into the atmoshpere.... as strange as this may seem. Because pump motor heat is wasted and not utilized to heat water, all of the heat in the spa water comes from the electric heater. The electric heater, at 5,500 watts, is by far the most expensive spa component to operate.
When a blower is added to one of these spas, energy efficiency goes from marginal to worse. The blower will be blowing cool air into the electrically heated spa water. A few minutes of the blower will cool the water down to the point where the electric heater comes on again. 5,500 watts! As a result, almost none of the full foam designs include a blower. This is unfortunate as a blower (or turbo air) is one of the best features to have on a spa.
Last point of this short article. When the entire under spa cavity is filled with foam, two things happen. First, there is a thick layer of foam under the spa. Remember heat rises. It goes up. Insulation on the bottom is of the least importance in insulating the spa. Remember it was put there to hold up the spa shell and not really for heat retention. Secondly, there is only a thin layer of foam higher up in the spa walls. The vertical side walls are perhaps 5 inches of foam wide at the most. Those upper walls hold water pipes and only 1 inch or so of foam separates the pipes from outside atmosphere. Heat will escape through these side walls and protect those pipes (as well as the equipment bay) during freezing weather. But, for how long? We don't have to worry about this at all here in Hawaii. But, we do need to be very concerned with energy efficiency here due the cost of electric power..