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Posted by john cockerill on December 26, 2003 at 20:29:54:
In Reply to: Re: What are the advantages to a cold start aquastat? posted by Joe on December 22, 2003 at 08:58:57:
: Cold start more applies to a boiler that has to run durring the summer to service an indirect hot water tank. If you have a tankless coil you can't do it. Many cast iron boilers will get too much condensation and soot up, especially if they're high mass. Will take too long to come up to temp to service an Indirect hot water tank. Better option is warm start, let the boiler drop to 120 degrees.
: This works better on well insulated 3 pass boilers, since they're slower to cool down. Durring the winter the boiler will need to fire for a heat call anyway every few hours or so. True cold starts are unlikely then anyway.
: Usually low mass steel boiler can run cold start since they can ramp up quicker and steel takes the stress better. You won't get 30yrs out of them though.
Exquisite Heat BTU Delivery System
The challenge to economy and comfort has been the search for a method to deliver BTU’s to a space requirement in the most efficient way. First is to define what efficiency is. Efficiency is a twofold concept. First is to operate HVAC equipment with just enough fuel to deliver the correct supply of heat to meet the energy loss, to the enclosed space. The second requirement is to distribute that heat in a way that produces even steady comfort. If this is done it is estimated that 5-12% fuel conservation could be accomplished. It stands to reason that a steady supply of comfort would detract from the feeling to need to change thermostat settings by occupants. If occupants could count on a stable temperature, they would be discouraged from changing thermostat settings. Occupants may be satisfied with a slightly lower setting. If reliable lower temperatures were provided, occupants would be better adaptive to lower temperatures. It is also estimated that 2-3% energy conservation can be achieved for every degree of reduction in thermostat settings. Tremendous waste occurs when thermostats are set high when someone is chilly and not reset back. Occupants become accustomed to excess temperature and feel chilly when the temperature is set back to optimum comfort settings. Unstable temperature leads to over correction in temperature settings. The system is both inefficient and uncomfortable.
How then do we provide the ideal case? 1. Stable Temperature. 2. Even circulation. 3. Lowest source temperatures.
The first issue is even circulation of transfer medium for even comfort. This has in the past been accomplished with constant circulation of heated medium. This provides a constant temperature to the building at a proper temperature. The method for establishing this operating temperature has been manual calibration of out door boiler reset devices and algorithms that estimate the difference between outdoor temperature and the heat load of the building. The difficulty with these devices is that the real performance of the system components is not connected. Components often miss their target temperature and the error is compensated for by short thermostat cycles, or full circulation of a lower than necessary temperature which falls short of the comfort requirement. Worse yet is continual circulation of overheated transfer medium. Many reset devices are disconnected for these reasons. To overcome this dilemma the reliability of Internet feedback is used to make correction to the inevitable errors systems currently suffer. All this is a complicated, disconnected, difficult to mange and uncomfortable process. There is a need for a process of adjusting transfer medium output temperatures, which is complete and self-learning within the total system itself. The system needs a way to teach itself the demand needs of the occupants.
Taking a total view of the HVAC systems, it would seem the first area to examine is that of the thermostat. The thermostat serves to communicate the comfort level desired by the occupants. It would also appear that the best indicator of real building heat loss and gain would be through sensing by a properly located thermostat or temperature sensor. Sunlight, wind, occupant levels, and outdoor temperature swings all eventually show up from within the building envelope at the thermostat. So why not use the thermostat as the guide to circulate the transfer medium evenly throughout the structure, as well as determining the ideal temperature for the transfer medium to meet the heat loss or gain within the building? If this can be done we can get away from complicated, expensive and uncomfortable methods to correct a disconnected approach.
We have to add a couple of factors to the heating equation that have been overlooked in previous models. The previous first assumption was that 100% circulation is needed for comfort. Actually thorough circulation of proper temperature transfer medium can be accomplished with 70% circulation. An additional factor to consider is time. If we supply a transfer medium temperature to a structure the thermostat will call for heat based upon the setting of the thermostat temperature and the temperature of the medium. When the comfort level is met the thermostat will discontinue the demand call. The goal then becomes adjusting the temperature of the transfer medium in order to have the thermostat deliver comfort while calling for heat 70% of the time. To measure call for heat “for 70% of the time” we need to study the thermostat history over time. We can do this by establishing an analysis time of say 90 minutes. We study the thermostat activity by polling the thermostat for demand every 5 seconds. Over 90 minutes this will provide 1080 samples. The numbers of positive results say 900; will yield a thermostat demand activity of .83 or 83%. If we compare the .83 to the desired .70 one could easily conclude that the thermostat is demanding for more heat. If the transfer medium temperature were raised to a higher temperature, this would satisfy the thermostat at 70%. A proportional adjustment in accordance with the difference of analysis findings would present a closer approximation to the best temperature for transfer medium to meet the requirements or demand of the thermostat at 70% circulation. Over successive periods of analysis, the transfer medium temperature would be put through upward and downward adjustments in direct relation to the heat loss and heat gain of the structure under changing environmental circumstances. Using a microcontroller, the thermostat activity can be gathered, temperature of boiler output can be measured, and control of output temperature or fire times to the building is accomplished. This method can be employed for all methods of HVAC. This process accomplishes one more feature, which is important to comfort. It removes all lags in the system. The demand and satisfaction process are all taking place at the thermostat. The thermostat with the microcontroller take all things into consideration providing all the information that is necessary to deliver smooth comfort at optimal levels of efficient energy use.
John Cockerill. Exquisite Heat www.exqheat.com US Pat. 6,402,043
P.O. Box 155 Scarsdale, NY 10583 Tel 914-723-8403
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