Posted by Dave Gavin:
Click on table to enlarge.
The table above details the energy consumptions of natural gas and electricity for the OpenAire structure and the current bubble. This is one of many comparative analyses we did for various structures and operating conditions, and cost of energy. Note the significantly larger amount of natural gas required to heat the bubble. This is because of the large volume of heated air required to keep the high domed structure inflated, and the leakage at the vents, airlocks, and grade beam.
The solar credit also favors the OpenAire structure, as does the lower lighting requirements. Cogeneration is a big plus. Some of the other items are significant consumers of energy, put as they need replacement in the future more efficient technology can be applied.
Dave Gavin, Lew Cohen, Bill Kunde , Pool Evaluation Subcommittee
My understanding was that little to no dehumidification was going to be needed with the OpenAire structure. Please explain the energy consumption related to this in your analysis.
ReplyDeleteTaking a cogen credit for OpenAire and not the existing (or future) bubble distorts the advantage of the permanent enclosure.
ReplyDeleteAlso, we need to be clear that cogen doesn't save energy; it just saves energy cost (hopefully).
Cogen does indeed save energy because fuel is used more efficiently. Electricity from a power plant is in many cases generated by burning coal, gas or oil, a portion of the heat is used to boil water to make steam-the rest goes out the smokestacks. The steam is used to power a turbine to make electricity. The electricity may travel 100's of miles, with energy losses, to the use point. The overall process may be 35-40% efficient. With cogen, you create the electricity on site using a gas-fired reciprocating engine that powers an electric generator, this eliminates the transmission losses...and you collect the heat from the process and use it to heat water and space, thus lowering your need for gas fired space heaters. Overall, your cogen energy efficiency is over 85% verses about 35% for power plant energy. On top of that the gas would be sold to us at below market price.
ReplyDeleteYes, Rich, the cogen could be used in conjunction with a bubble structure. It would have to be properly sized for the larger energy load. In my mind, it would be newer technology supporting wasteful use of energy.
ReplyDeleteRegarding dehumidification, we visualize that during the summer and parts of spring and fall the facility would operate in an "open" mode-roof open and side sliders open. This takes advantage of the "chimney" effect of natural circulation. In the cold weather seasons the building would use some mechanical dehumidification to control condensation. Since 5-6 air exchangers per hour are coded, a good portion of the dehumidification is handled with fresh air influx, this air is heated in part by heat recovery in the HYVAC system. Perhaps Lew Cohen would like to clarify further.
ReplyDeleteIs the presentation that was given at the public hearing going to be posted on this site?
ReplyDeleteCogen may be more efficient than a central plant, but it doesn't reduce energy consumption at the site. It just changes the source (and hopefully the cost) of the energy used. Instead of buying kWh from CL&P (or a third party) we would make it onsite. Instead of burning gas in a boiler to make hot water we would use recovered heat from the engine (or microturbine), which should reduce cost, but it won't change the number of Btu's needed to heat the water or the space above it.
ReplyDeleteDave:
ReplyDeleteif dehumidification is going to be handled by opening the roof and walls, why is there 169,223 kWh associated with it?
If it is more efficient, it has to save energy somewhere-if I use energy more efficiently, I use less-right-if not at the site, somewhere, no?
ReplyDeleteOnly during the 5 or so months after spring, summer, fall- some mechanical dehumidification may be required when the roof is closed during the others to conserve heat, to control possibility of condensation. Significantly less, over 12 months than a more enclosed structure that is less efficient during summer open ventilation.
ReplyDeleteDave - Regarding the efficiency of cogen plants, you're comparing apples and oranges.
ReplyDeleteIt's true that onsite generation is more efficient than a utility central generating plant, due to heat recovery (if most of the heat is recovered most of the time). Utility generating plants generally do not recover waste heat (except combined cycle plants where some waste heat is used), plus there are the transmission line losses.
The pool facility is going to have a set amount of energy consumption (lighting, HVAC, hot water, DHW, etc.). These Btu's are not going to be reduced by cogen. The only way to reduce/minimize them is through the initial building design and ongoing energy management.
Having said that, cogen may reduce the cost of these Btu's by recovering the waste heat and putting it to good use, but when everything is factored in, including the O&M costs and capital costs (initial/replacement), the economics are usually touch and go.
The main advantage of cogen is reliability.