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Posted by HeatPro on July 08, 2007 at 11:46:06:
In Reply to: Re: Ergomax or equivalant posted by Dee on July 07, 2007 at 22:46:19:
Have you seen a study or calculation based on this "does cost more...more energy is invested?" Something based on average house hold usage. And then have you heard of back-feeding this into your water-systems' overall "efficency"?
+++ Studies of this kind are done at the Department of Energy under the Annual Fuel Utilization Energy program (AFUE). AFUE testing is one to approximate an average water temperature of 140F for the year. There is also a test for low-temperature as the AFUE 2000 test. This is for "typical conditions." As most boilers come from the factory at 84% AFUE or better and temperatures over 150F prevent most condensing their ranges are within 3%. This is not good for the marketing managers who've made marketing ads based upon efficiency improvement by buying their product over other boilers - they have to cast for new "pitches."
Let me reword my question like this:
Current radiant system runs water at 180 degrees.
Current hot potable water heater runs water at 120 degrees.
New radiant system runs water at 180 degrees.
New exchanger outputs hot potable water close to 180 degrees. Which requires it to be cooled down with a mixing valve.
+++ Aside from the meaning of "Radiant" which muddies your question, as radiant USED TO mean baseboard at 180F in the coldest weather which has a 20% radiant component and 80% convective component, "Radiant" today more often means floor heat which runs at a max of 140F in the coldest weather and is part of the cause for the change to AFUE 2000 test which is called a lower temperature test. Thus I can't tell what you intend. Merely defining which radiant system can make some difference, and as typical "radiant" systems today run both boiler and max heating water at the same max temperature, there could be no difference.
Have you seen a study or calculation based on this "does cost more...more energy is invested?"
Again - "typical" is in the eye of the beholder. When considering sosts, consider fuel. Gas and oil are "typically" 1/3rd the cost of electric because electric generators waste 1/3rd of the fuel to make the electricity in the generator.
: For simplicity all three device run at the same efficiency (AFUE).
+++ As seen, boilers tend to run at close to the same efficiency. It is the storage device that holds the hot water that makes waste. A separate water heater can be made to heat the water as well as any other 'boiler'; but the AFUE test considers cooling time of the boiler, so a water heater is at a disadvantage as it isn't made to cool down, so tanks don't have an AFUE, so are studied to include storage losses - very often 35% waste. So we have to know what is the most typical - storage tank or not and which one of thoseis typical.
: If "current" system was considered optimal what would "new" system be considered in a percentage of the "current" system.
+++ The other part of the problem is what is a "system" and which one? As there is no "typical" home, you can't predict what system either. You could consult Housing and Urban Development department studies, as they try to predict costs for construction and operation for heat and hot water as part of their jurisdiction; but their concentration could hardly be considered for "typical" homes.
A 'typical cost' for making and using 70 gallons of hot water by the famous 2.5 people family is about $1400/yr for electric and $500 a year for gas or oil hot water. All your studies would arrive at maybe $200 a year difference for a family. Some question as to whether being able to have a family quarterly visit to Big "Mac or not.