Design for the Environment/Residential Heating and Cooling in Ontario

This page is part of the Design for the Environment course

Project Information

The purpose of this article is to explore alternative methods of residential heating and cooling that have not yet gained significant public presence or awareness, with the end goal of identifying the most advantageous alternative, with respect to function, environmental impacts (judged by EIOLCA and SLCA), cost and societal concerns.

Section 2 - Group B1

Yufei Man (manyufei)

Owen Moffitt (takata)

Steven Nadeau (nadeaust)

Alternatives

Ground Source Heating

Ground source heating/cooling utilizes thermal energy from the earth to heat or cool a house. Unlike the temperature of air which fluctuates throughout the seasons, the temperature slightly below ground is consistent year round. A geothermal system utilizes this phenomenon to control the temperature of the house. The system consists of three elements: an underground piping system, a heat pump and a distribution system for the house. During wintertime, the temperature below ground is warmer than in the house. This heat is absorbed by the fluid in the underground pipes which circulates to the house. The heat pump utilizes refrigerants which extract this energy and distributes it through the ventilation system of the house. During the summer, this process is reversed. The heat pump extracts the thermal energy from the house where it gets sent below ground. In this configuration, the earth acts as a heat sink. A ground source heating/cooling system only requires a small amount of electricity to power the heat pump which is why it is so efficient. Unlike traditional systems, the heat is not created through a combustion process but simply extracted from the ground.

Thermoelectric Solid State Heat Pump

A thermoelectric (TE) solid state heat pump operates based on the Peltier effect, in which electrical energy is converted to thermal energy. A thermoelectric module consists of a thermoelectric material, typically semiconductors such as Bismuth telluride (Bi₂Te₃), sandwiched between two ceramic plates joined with electrical interconnects. When a voltage is applied to the device, heat is transferred from one side to the other, typically against the temperature gradient. The direction of heat travel depends on the sign of the voltage, and thus the device is capable of providing both cooling and heating. The term “solid state” refers to the fact that the device has no moving parts, thus enabling it to run fairly quietly and requiring minimal maintenance.

TE heat pumps operate purely on electricity, so precise temperature control can be achieved as we can directly measure and control the current flow into the system. To date, TE solid state heat pumps are primarily used in cooling applications, whether it’s for electronic components that require specific constant temperatures, or portable coolers for personal use. Large scale applications however, in this case the heating and cooling of an entire residential house, are extremely rare or almost nonexistent, due to the potential cost and complexity of the overall system.

Highlights and Recommendation

SLCA

The SLCA analysis yielded inconclusive results, as the differences between the scoring of the two alternatives was too low to warrant definitive assertions. Furthermore, the SLCA failed to signify the most marked difference between the technologies of all: energy use during process operation. This was represented by a single matrix value, which only contributed to a difference of 2 out of 100 in the gross SLCA score. From the perspective of the EIOLCA and cost analysis, this is an inexcusable oversight. For this reason, the SLCA score is an inappropriate means of comparison. What it did accomplish, however, was to establish the general differences between the alternatives, which were verified with greater rigour in the quantitative analyses.

EIOLCA

The EIOLCA produced much more quantitative and useful results, which proved to be highly illuminating. Refering to the EIOLCA data, it is definitively clear that the process operation phase dominates the environmental impact. For example, the process operation phase accounted for 87% of the total GHG emissions released throughout the life cycle for ground source heating, and a staggering 97% for TE heat pumps. The same trend can be noticed in terms of all environmental metrics in the EIOLCA. Comparing the environmental outputs of the two alternatives, we see a very marked difference. In terms of every environmental metric, TE heat pumps have approximately 6 times the impact of a geothermal system over a lifetime of 50 years. This discrepancy is so high that it is a significant, if not a deciding factor in our analysis.

Cost Analysis

The cost analysis reveals an identical trend. While the startup costs for geothermal systems are significantly higher, the variable cost of process operation is over 6 times higher for TE heat pumps. Taking the present value of money into account, the cumulative cost of a TE heat pump over the course of a 50 year lifetime becomes roughly 3 times greater than for a geothermal system over the same lifetime. This is still a hugely significant factor.

So with respect to every analysis thus far, geothermal systems have proven far superior. As the duration of system use extends beyond even half a decade – far below the total life of the system – geothermal emerges as victorious with respect to both cost and environmental impact, at a significant order of magnitude.

Societal Analysis

The only caveat to this otherwise flawless victory is the special societal considerations required for ground source heating. The comparatively high initial investments as well as the invasive installation procedure are significant barriers to overcome.

Conclusion

Ultimately, it is the users’ decisions to that decide whether or not this alternative spreads as a viable alternative to current heating and cooling methods. As a major stakeholder in the economic and environmental demands of its citizens, it is recommended that governments introduce adequate funding and programs to help accomplish this goal. If the initial investment can be made by a willing party, the overall impact for all stakeholders is significantly lower costs and environmental demand.

Functional Analysis

Ground Source Heating

Ground source heating energy flow schematic

Ground source heating takes advantage of free geothermal energy – it comes from a virtually infinite reservoir. Electricity input is only required to bring the geothermal energy to a usable temperature. As a result, the efficiency of the heat pump in this system is actually greater than 100%. For every joule of electricity inputted, more than one joule of heat is outputted due to the contribution of the ground heat. This is a highly effective use of cascade approach –use a low quality energy source input to yield a low quality energy source output, resulting in minimal waste in energy conversion. Based on this qualitative analysis alone, we can expect that the operating energy demand will be lower than for TE heat pumps. However, as mentioned previously, installation is invasive and we can expect the fixed costs (both economic and environmental) to be higher.

Thermoelectric Solid State Heat Pump

Thermoelectric solid state heat pump energy flow schematic

In contrast, a TE heat pump has only a single input; electricity – and you have to pay for every joule. This means system efficiency, while higher than natural gas heaters, is below 100%. Electrical energy is also a high quality energy source, so its use to yield a low quality energy output is not ideal. Since a TE heat pump functions as a standalone unit, however, fixed costs are anticipated to be lower, at the expense of a higher variable cost of operation.

EIOLCA (Economic Input-Output Life Cycle Assessment)

Ground Source Heating

EIOLCA outputs for ground source heating

Geothermal systems require very little power to run during the use stage. For this reason, the primary polluting stages are the pre-manufacture and manufacturing phases. The piping used to gather the underground heat is made of HDPE. The extraction of the petroleum required to make these pipes is energy intensive and requires metal machinery which release large amounts of greenhouse gases and toxic emissions. The heat pump contains metallic parts such as steel and copper which emit many toxic emissions when they are extracted and smelted. Also, the installation of the piping requires digging large trenches to bury them. This process requires metallic machinery as well as large amounts of energy which cause large amounts of pollution, primarily in the form of GHG’s and toxic emissions.

However, once the system is in place, very little is required to make it function. A relatively small amount of electricity is needed to power the heat pump. This electric requirement is the only source of emissions for this stage. Over an assumed fifty year lifespan, the emissions of the geothermal system are lower than for a thermoelectric system across the board.

Thermoelectric Solid State Heat Pump

EIOLCA outputs for thermoelectric solid state heat pump

Thermoelectric solid state heat pumps do not require a significant amount of resources to produce. Therefore, the premanufacturing and manufacturing stages account for a very small portion of the total emissions and energy requirements. Not only are TE heat pumps relatively small compared to a geothermal system, but most of the constituent materials can obtained from either recycled sources, or as by products of other material extraction/refining processes. In terms of product distribution, most products are simply transported via trucks across North America, accounting for the small percentage of total emissions and energy requirements.

Naturally, with a lifespan of 25 years, the process operation stage occupies the vast majority of the product lifecycle. Since TE heat pumps require only electricity, a unit would require a significant amount in order to be able to heat/cool an entire household. This high demand for electricity would have to come from power plants, many of which burn fossil fuels. Over a period of two lifespans of 50 years, the high amounts of fossil fuels burned to generate the required power would result in enormous emissions and energy requirements, most notably the incredibly high greenhouse gas output, as power plants account for approximately 25% of the world’s total carbon dioxide emissions.

When the unit has reached the end of its life, it can simply be disposed of like any other household appliance. Being no bigger than a typical natural gas furnace, the user can simply drive the unit to a nearby waste disposal facility, where it is disposed of like any other old appliance. Such a common process does not have emissions or energy requirements that would be significantly higher than for other heating/cooling units such as geothermal or natural gas and air conditioning.

Compared to a geothermal system, a thermoelectric system definitely results in higher greenhouse gas/toxic air/conventional air pollutants emissions and total energy requirements over a period of 50 years.

SLCA (Streamlined Life Cycle Assessment)

Based on the totals alone, we see that the two alternatives score very comparably, at 61.5 and 64.5 out of 100, respectively. A 3% difference is not significant and does not warrant a judgment in favour of TE heat pumps. However, we can compare the SLCA values by subtotal to see where the differences and similarities lie.

Both alternatives perform very poorly in resource provisioning, due to the large number of extraction processes required to obtain the raw materials, particularly the variety of metals in thermoelectric devices, and in the case of ground source heating, the use of petroleum products for the pipes. TE heat pumps outperform ground source heating marginally in the production stage, due to the use of refrigerants in ground source heating that can evaporate and act as greenhouse gases. This happens again in the distribution and process implementation stage, due to the high energy cost associated with digging and laying the pipes that are specific to ground source heating. Ground source heating’s high efficiency allows it to outscore TE heat pumps in the process operation stage. In fact, it should be noted that it receives a perfect 20/20 score during this stage. This should be given special consideration, as the long life of heating and cooling systems make the process operation stage one of the most crucial factors on environmental demand. While purchasing and installation of each alternative may only require days or weeks, the process operation stage goes on for decades.

Ground Source Heating

	Material Choice	Energy Use	Solid Residues	Liquid Residues	Gaseous Residues	Total
Resource Provisioning	2.5	0	0	0.5	1	4
Production	2.5	2.5	3	3	2	13
Distribution and Process Implementation	2.5	0.5	2.5	4	2	11.5
Process Operation	4	4	4	4	4	20
Refurbishment, Recycling and Disposal	2.5	2.5	2	2	4	13
Total	14	9.5	11.5	13.5	13	61.5

Thermoelectric Solid State Heat Pump

	Material Choice	Energy Use	Solid Residues	Liquid Residues	Gaseous Residues	Total
Resource Provisioning	2.5	0.5	0	0	0	3
Production	3.5	1.5	3.5	3.5	3.5	15.5
Distribution and Process Implementation	2.5	3.5	2.5	4	2.5	15
Process Operation	4	2	4	4	4	18
Refurbishment, Recycling and Disposal	1.5	3.5	2	2	4	13
Total	14	11	12	13.5	14	64.5

Cost Analysis

Ground Source Heating

The initial cost of a geothermal system is quite high ranging from $22,700 to $47,700. These costs include the digging of the trenches, the purchase of the heat pump and the upgrade to the ventilation system. The price varies depending on the size and location of the home. However, the operational cost is very low at about $1000 per year. This amounts to about 36% of a traditional natural gas system. Therefore, the money saved versus a traditional system allows the cost to be recuperated within 4 to 10 years, and thus in the long term, the purchase of a geothermal system can be profitable.

There are also other benefits to the installation of this system. Financial incentives can be obtained depending on the governmental regulations in the area of the house. Furthermore, the installation of a ground source heating/cooling system increases the value of the house since it has such high long term benefits.

Comparative cumulative costs over a lifetime of 50 years

Thermoelectric Solid State Heat Pump

Since there were no thermoelectric modules of such scale currently on the market, we had to estimate and extrapolate to determine a suitable price for a TE module to heat/cool an entire house. Given that typical natural gas furnaces range from 40,000Btu/h to 150,000Btu/h, we will use 90,000Btu/h as the average required output of a residential heating unit. 90,000Btu/h amounts to about 26,400W of power, which is required to flow across the heat pump. Based on a manufacturer quote of $12CAD for a 140W module, a TE module that outputs 26,400W of power will cost approximately $2,260CAD. Factoring in the cost of a heat sink and other miscellaneous components, we have decided on $2,400CAD as the average price of a unit.

The most efficient thermoelectric devices can achieve up to 17% Carnot efficiency. Houses built from 1946 to 2006 have an average annual gross thermal output requirement of 65GJ (18,000kWh), meaning that the total energy put into the system is near 106,000kWh. At current electricity rates, taken from Toronto Hydro Electric System electricity bill, of $0.056/kWh for first 2,100kWh, and $0.065/kWh for beyond that, we are looking at an annual cost of about $6,871(CAD) to heat/cool a home purely using TE heat pumps.

For a thermoelectric system, the initial cost of $2,400 may be seemingly low compared to that of a geothermal system. Over time, however, annual costs of $6,871 will accumulate, eventually becoming much more of a financial burden than would a geothermal system. In fact, it only takes five years for a geothermal system to become more economical overall than a thermoelectric system, as shown in the graph.

Societal Analysis

One significant concern that is not accurately captured by quantitative analysis is the effect on desirability of the two technologies from their vast difference in price and convenience. A thermoelectric system requires minimal capital investment and non invasive installation. A geothermal system, on the other hand, requires extensive investment and large scale renovation. This will cause resistance amongst some users, making widespread adoption of this technology more difficult. Economic and environmental savings can only be realized once the initial large scale investment has been made.