Combined Heat and Power Plant for a Community

(And Air-Conditioning Too)

Generating all of the electricity, cooling and heating on a community-scaled basis benefits both the environment and pocketbooks of those living in the area. By integrating a natural gas turbine engine into a community to provide all the energy needs, electric and thermal, the efficiency can be maximized while to consumer costs can be minimized. Since most homes in America are dual use for shelter and long-term investments for the inhabitants, the initial capital costs can be spread out over many years of annual savings over the traditional single-home transmission lines, air conditioning and heating systems.

DCMC Power Plant

Example of a District CHPP at Dell Children’s Medical Center [1]

Two analyses need to be made from a technical standpoint to understand the viability installing a small, district combined heating and power plant (CHPP). First an analysis must be performed to find the expected electricity, cooling and heating load subjected to the power plant by individual homes. The second is an engineering analysis made of the capacity of a standard gas turbine engine, absorption-cooling system, electric chillers and exhaust heating system. The final analysis is made from a policy standpoint to match the loads and capacities experienced by the community and power plant respectively, to maximize efficiency and minimize costs to make the proposal viable.

Home Load

Image

[2]

The load experienced on the power plant is different from the capacity of the power plant. The load refers to how much power or energy is needed from the home in order to operate on a normal basis. The capacity refers to the ability of the plant to produce an electrical or thermal load. There are many sources to find the load of an average house but several suggestions can be made to aid in this analysis.

It is easy to assume that a combined heating and power plant would likely find its success first in an upper class neighborhood. By this reasoning the average values of power and energy can be found for households making over $75,000 a year. This assumption is made on the basis that middle to upper income earners could more easily shell out excess cash towards a green or self-sustainable community. Secondly the heating and cooling loads averaged over a year should reflect the seasonal changes. Homes do not need heating and cooling at all times in the year. Therefore the loads found can probably be multiplied by a value of 4 to find a general estimate of the heating demanded in the winter months and the cooling demanded in the summer months. Obviously this estimate should be made to reflect the geographical location for the home load analysis. The more specific location assumption can be made, the more accurate the analysis can be for a specific region. Once the load is found, the capacity can be explored.

Power Plant Capacity

Power plants in general must be analyzed with a thermodynamic model. A gas turbine engine has been chosen for this analysis since it is currently a cheap, abundant and relatively green source of energy. It is analyzed using various assumptions as a regenerative, non-ideal, air-breathing Brayton cycle with irreversibilities. Regeneration of the exhaust stream to heat up the inlet stream aids the combustion process of heating up the air for the turbine. The Brayton cycle is non-ideal and includes irreversibilities since the compressor and turbine do not work 100% ideally as there are frictional and fluid losses. The air flowing through the system can be modeled as a mixture of gases undergoing compression, combustion and expansion. For the electricity the turbine is simply attached to the electric generator on the same shaft. This is the basis for an analysis of the engine, which produces exhaust temperatures high enough (700 F range) to operate heaters or air conditioners. Heating is accomplished simply by running the hot air past a water stream or loop in an exchanger where the water is then distributed to the community as hot water. The air-conditioner works in a similar fashion to the air conditioner in a car. The exhaust heat drives a type of vapor-compression cycle, which in turn can produce chilled water at 44 F that is then distributed to the surrounding homes. By running these pipes in the walls of a house, and/or exchanging the cold/hot streams with an air stream can produce heating or cooling in each home.

Comparison

Typical Power Delivery for normal hospitals in Texas

Typical Power Delivery for normal hospitals in Texas at DCMC [1]

Power Delivery at Dell Children's with the District CHPP

Power Delivery at Dell Children’s with the District CHPP [1]

To conclude on the viability of a district power plant to provide heating and cooling in a community, a full analysis of the loads and capacities of a typical home and power plant must be made. The power plant can then be scaled to fit a certain amount of homes as to make it economically viable. This is where a policy discussion of the economic cost-benefit analysis must be made. What are the capital costs? What are the annual expenses? Finally, what benefits to the pocketbook of the homeowner does a system like this have? I think a system like this is in our future. In all reality, the main question is, can we do this now? I hope to be able to devote time to fully analyze the benefits and costs of such a system as to decide on the viability of such a project.

[1] Collins, Jim. “Case Studies: Mueller Energy Center at DCMC Austin, Tx.” CHP Conference 2011. N.p., 03 Nov. 2010. Web. 14 Apr. 2013. <http://www.chpcon2011.com/Portals/24/Events/CHP_trade_show_2010/Presentations/Collins_Mueller.pdf&gt;.

[2] “U.S. Energy Information Administration – EIA – Independent Statistics and Analysis.”Residential Energy Consumption Survey (RECS). N.p., 28 Mar. 2011. Web. 14 Apr. 2013. <http://www.eia.gov/consumption/residential/reports/2009/electronics.cfm&gt;.

Advertisements

Leave a comment

Filed under Uncategorized

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s