Content area
Full Text
ABSTRACT
The vapor vacuum-heating (VVH) technology employs the heat pipe concept for heat distribution in buildings. Heat pipes ' superior efficiency and reliability can be utilized with regular and condensing boilers as well.
Today 's technology employs only hot-water condensing boilers. In order to keep energy efficiency above 90% in a hotwater system with a condensing boiler, hot water should be circulated through the condensing section at a temperature not higher then 100°F (37.8°C). Alternatively, a VVH and condensing boiler combo can work efficiently in a broad temperature interval without such limitations.
Compared to a hot-water heating system, VVH is healthier and more comfortable (radiant heating versus convection), more reliable (no moving parts), dependsless on electricity, is safer (vacuum versus 30-100psig [0.207-0.69MPa] pressure in high-rise buildings), produce no damage from leaks, can be stopped in winter without frozen pipe problems, operates in a broad interval of temperatures, and allows more granular control of the heat distribution. Installation cost comparison is also in favor of VVH: for new installations 40% in savings is estimated and for the retrofit of steam-heating systems, up to 70%> in savings can be achieved due to easier plumbing and salvaging of an existing boiler.
INTRODUCTION
We can't solve problems by using the same kind of thinking we used when we created them.
-Albert Einstein
In order to improve energy efficiency, modern condensing boilers absorb the latent heat of water vapor from flue gas. Over the past decade, a large number of manufacturers have designed new boilers which are capable of operating in condensing mode and, therefore, offer higher efficiencies. These boilers can be fire-tube, water-tube, cast-iron, or cast-aluminum design. In the UK, noncondensing boilers were practically extinct by 2010 (Eljidi 2010). The percent of condensing boilers sold in the U.S. has been steadily rising from 5% (in 2004) to about 25% (in 2010) (A.O. Smith 2012), and the trend continues.
Figure 1 (ASFIRAE 2008) shows the effect of the inlet water temperature on boiler efficiency, dew point, and the condensing range (ASHRAE 2008). At the 15% average water volume content in a flue gas (DOE 2014), the corresponding dew temperature of 130°F (55°C) is a break point (Engineering Toolbox 2012).
The entering water temperature and boiler load are critical factors...