Design for the Environment/Residential Heating and Cooling

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This page is part of the Design for the Environment course

Due to home heating and cooling, humans have settled in harsher environments which were previously inhospitable. To make a house comfortable for living a certain amount of energy is required to raise or lower the home temperature to match the recommended living room temperature.

A single-family home.

The recommended living room temperature has been taken to be 21˚C (West Midlands Public Health Observatory) [1]. In this analysis it will be assumed that cooling is only required for June, July and August and heating is required the rest of the year [2].

The average household considered in this analysis has a floor space of about 1,200 sqft, and it will be used as a reference. The average house having a floor space of 1,200 sqft will use about 89.62GJ of energy in a year [3] out of which 60% is used on home heating and about 5% is used on home cooling [4]. From the information collected above we can conclude that about 53.76GJ of energy is used on home heating and about 4.481GJ of energy is used on home cooling in an average household having a floor space of 1,200 sqft in one year.

Our group for the Design for the Environment course will compare different ways of home heating and cooling and try to find the alternative that is not only the most environmentally friendly but also the most cost effective. Monarch Construction has been chosen as the client in this analysis. The company is involved in the construction of separate homes and well as high rise apartments around Toronto. This article will compare home heating and cooling by natural gas furnace and electric air conditioner, evacuated tube collectors and GHP (geothermal heat pump). Currently, natural gas furnaces and electric air conditioners is the most widely used method for home heating and cooling.

Project Information[edit | edit source]

MIE 315 Section 1, Group A10

  • Tasnim Ahmed (Tasnim)
  • Gundeep Dorka (ginnidorka)
  • Michael Lau (laumich4)
  • Varun Malik (malikvar)

Background Information[edit | edit source]

Recycling symbol.svg

Currently home heating is done mainly by natural gas furnaces and home cooling is mainly done by electric air conditioners. These mainstream home heating and cooling systems have considerable environmental impacts, therefore there is need for developing more environmentally friendly alternatives. Investements into research for developing renewable sources of energy particularly evacuated tuble collectors and geothermal heat pumps will facilitate the developement of such alternatives.

For natural gas furnace, a gas fired condensing system is going to be analyzed. An induced draft burner is used in this system where a motor driven fan or blower is used to create a partial vacuum to draw in air [5]. The air mixed with Natural gas is burnt in a gas burner and the heat is exchanged via a stainless steel heat exchanger [6]. A natural gas furnace provides rapid heat delivery, have low operational costs and are capable of circulating the air inside the house. However, the ducts related to natural gas furnaces are difficult to service and maintain. Burning natural gas for heating also has substantial greenhouse gas emissions.

A condensing furnace

In a electric air conditioner a refrigerant is used. Heat is absorbed and released when the refrigerant changes between liquid and gas state. Heat is absorbed when it changes from liquid to gas, and releases heat when it is returned to liquid from gas. The moisture is removed from the air, when it contacts the indoor coil, which is collected in a pan at the bottom of the coil and sent to a house drain. Electric air conditioners eliminate the need to install additional dehumidifiers. Even though newer air conditioning systems are highly efficient, most of the systems in use are highly inefficient. One of the major issues with electric air conditioners is the harmful effects of the refrigerant CFC (Chlorofluorocarbon) on the ozone layer.

A geothermal heat pump uses earth as a heat source when operating in heating mode or a heat sink when operating in cooling mode. These systems are based on the stability of underground (shallow ground - about 10 ft deep) temperatures. Temperatures range from 10°C - 16°C. Thus this reservoir can act as a heat source in winter months and heat sink in summer months. EPA (Environmental Protection Agency) has called geothermal the most energy efficient, environmentally clean and cost effective space conditioning systems available [4]. GHP systems take minimal surface ground space as piping is routed underground to the mechanical room. GHPs also improve humidity control by maintaining above 50% relative humidity, making them very effective in humid areas [7]. It is plagued by extremenly high installation costs as a typical residential size geothermal unit would cost about $9000 [8].

For the purposes of comparing solar energy to natural gas, we will focus on solar heating systems via evacuated tube collectors. Solar radiation is collected and used to heat either a transfer liquid or air. The heated liquid or air is then stored for later use or circulated to heat the space immediately [9]. Solar collectors can also be used for cooling in the same manner. Heat collected by the evacuated tube can be used as the heat source needed to evaporate the refrigerant component of a refrigerant-absorbent fluid mixture [10]. The condensation of this vapor creates the cooling effect in the air [11]. It is essentially a renewable resource for the foreseeable future, since the Sun will still have enough energy for approximately the next 5 billion years [12]. There is no direct cost of using solar energy. Though the initial cost of the array may be a factor, solar cells last for long periods of time and require minimal maintenance [13].

Evacuated (or vacuum) tubes panel.

Recommendation[edit | edit source]

The recommended alternative for home heating and cooling depends on how each alternative fares on the different sections of the analysis.

Evacuated tube collectors use a renewable and clean source of energy being the sun which gives it a significant environmental advantage over natural gas furnace and electric air conditioners. From a functional point of view, we conclude that evacuated tube collector is the best alternative. The total cost including capital, operating and disposal for natural gas furnace and electric air conditioning system comes out to be $3867.98. The total cost including capital, operating and disposal for geothermal heat pump system comes out to be $41939. The total cost including capital, operating and disposal for evacuated heat collector comes out to be $19,343.45. Natural gas and electric air conditioning got a score of 53 while evacuated heat collectors and geothermal heat pumps scored 65 and 58 respectively. The societal issues for evacuated tube collectors are relatively minor compared to the other two alternatives, we can say that evacuated tube collectors are preferable from a societal point of view.

The total greenhouse gas emissions from natural gas furnaces and electric air conditioners, geothermal heat pumps and evacuated solar collectors are 36.426, 32.819 and 31.456 MT of CO2 equivalent respectively. The total toxic emissions from natural gas furnaces and electric air conditioners, geothermal heat pumps and evacuated solar collectors are 186.18kg, 78.391kg and 50.68kg respectively. The total energy usage for natural gas furnaces and electric air conditioners, geothermal heat pumps and evacuated solar collectors are 0.418 TJ, 0.088TJ and 0.0.785TJ respectively.

Natural gas furnace

& Electric air conditioner

Geothermal heat pump Evacuated tube collector
Functional analysis 6 8 9
Cost analysis 8 5 7
Streamlined LCA 6 7 9
EIOLCA 6 8 9
Societal analysis 6 6 8
Total 32 34 42

Values out of 10 (alternative having a value of 10 is better than alternative having a value of 8)

From the rating matrix above we can conclude that evacuated tube collector is indeed the better home heating and cooling alternative out of the three.

Functional Analysis[edit | edit source]

Natural gas heating & Electric Air Conditioning[edit | edit source]

A gas furnace consumes 410 kWh of electricity per year [14]. Of the required 53.76 GJ (14933 kWh) of energy for heating a natural gas furnace is required to produce 14523 kWh/year (49 554 530.713 Btu/year). Based on the assumption that 1 ft 3 natural gas is equivalent of 1027 Btu [15], it is calculated that 48251ft3 of natural gas will be used in one year. Since all natural gas furnaces have some loss of energy, there will be more natural gas and electricity consumption than this estimate. The additional usage is dependent on the efficiency of the model of furnace being used. For our analysis we are using a Goodman GCV90704CX gas furnace which has a 69,000/48,000 Btu Furnace Efficiency and a 93% Annual Fuel Utilization Efficiency (AFUE) [16].

The capacity to cool an area of 1,200 sqft will require an air conditioner with cooling capacity of 19000-24000 Btu/h [17]. This estimate is based on the fact that a temperature of 24°C needs to be maintained with a humidity level between 30 and 50 percent. An important criterion always for home cooling system is the efficiency which is measured by a seasonal energy efficiency ratio (SEER). The SEER of central air conditioners ranges from a minimum of 10.0 to a maximum of about 17.0 [18].

Geothermal heat pumps[edit | edit source]

Considering an average house size of about 1,200 sqft and the total energy usage in a given year for heating, cooling and hot water being roughly 76.161 GJ [19], a two ton GHP unit (equivalent to about 7 kW of energy) should provide sufficient energy (230 GJ under optimal conditions) during the peak months of January and July for heating and cooling respectively [20].

Significant energy savings (energy needed for the water pump, compressor, fan and controls) can be achieved through GHPs with reduction in energy consumption of 30-70 % in heating mode and 20-50% in cooling mode [21].

Evacuated solar collectors[edit | edit source]

The Canadian National Climate and Information Archive states the average annual value for hours of bright sunshine in Toronto to be 2037.6 based on the years from 1971-2000 [22] Furthermore, the NASA Surface meteorology and Solar Energy Tables state that the average amount of direct normal radiation in Toronto is 4.01 kWh/m²/day [23]. These values are higher during the summer months and lower during the winter months. Evacuated tubes are designed such that there is always direct normal radiation on the tubes throughout the day [24]. In order to achieve the assumed values of heating and cooling needs for a 12,000 sqft residence, more traditional sources of energy will be necessary. It is typical for an active solar system to be designed to supply 40-80% of a home’s heating needs [25].

Cost Analysis[edit | edit source]

Natural gas heating & Electric Air Conditioning[edit | edit source]

Provided below is the basic cost break down for natural gas heating and electric air conditioning. The cost values for the natural gas heating are based upon the use of the Goodman GCV9 model made by Goodman Air Conditioning and Heating [16]. The values for the electric air conditioner are based upon the use of the Goodman GSC 13 high efficiency air conditioner [26].

Natural gas heating

Capital Costs Operating Costs (20 years)
Item Cost Item Cost
Gas Fired Furnace $1276.99 [16] Natural Gas + Electricity $35700 + $483.80 = $36183.80 [27]
Ontario Rebate –$500 [28] Maintenance & Repair $2799.80 [29]
Total $776.99 Total $38983.60

Electric Air Conditioning

Capital Costs Operating Costs (20 years)
Item Cost Item Cost
Air conditioner $1135 [30] Electricity $1438.60
Ontario Rebate –$200 [28] Maintenance & Repair $2700
Total $935 Total $4138.60

Geothermal heat pumps[edit | edit source]

High initial costs often provide the biggest hurdle and prevent homeowners from switching to geothermal systems. However, most governments provide prospective buyers with financial incentives and rebates if and when they choose to purchase energy efficient systems such as ground source heat pumps. Furthermore studies have indicated that on average, GHP operating costs are up to 50% lower in comparison to traditional natural gas [31].

Capital Costs Operating Costs
Item Cost Item Cost
Parts & Labor (includes minimum duct work) $1000 Electricity/Energy Costs $16738 [32]
HDPE Pipe and Installation Costs $10000 [21] [33] Maintenance $2067 [34]
Geothermal Unit (–$2000 rebate) $7000 [31] [35] Parts Replacement $4000 [36]
Miscellaneous (Water Pump & installation) $800 [37] Disposal Costs $333 [38]
Total $18800 Total $23139

Evacuated solar collectors[edit | edit source]

The cost values for the evacuated tube collectors are based upon the use of GSE IS-195 product made by Globe Solar Energy, Inc [39]. There is no operating cost for an evacuated tube solar collector. It uses no external energy to run. But we can consider the cost of other energy sources to meet the necessary level of heating or cooling. At its highest efficiency a solar collector should only provide 40-80% of the year’s needed heat [40]. Based on this and the average price for natural gas, the effective operating cost for 20 years would be $16,065, using 45% supplied by natural gas.

Capital Costs
Item Cost
GSE IS-195 $2990
Installation Materials $300
Installation Labor $700
Ontario Rebate –$500
Federal Rebate –$500
Energy Audit 1 $300
Energy Audit Rebate –$150
Energy Audit 2 $150
Total $3290

Streamlined LCA (SLCA)[edit | edit source]

The streamlined SLCA is a semi quantitative analysis of the alternatives to find the best possible alternative. In this case two alternatives are compared with the baseline. To evaluate the different alternatives on same merits through different life stages, the product life cycle guideline was used.In this analysis a higher score means less harmful for the environment. The SLCA results revealed that evacuated tube collectors had the highest score and natural gas heat and electric cooling had the least points indicating the most and least environmental friendliness respectively. Following is a brief reasoning for the rating during different life stages.

Pre-manufacturing[edit | edit source]

It is noticed from the SLCA that all the alternatives received the same score for the pre-manufacturing stage. This is due to the common material usage (i.e Aluminum, steel).Wastewater from steelmaking has high contaminant levels and requires extensive removal and treatment [41]. Cokemaking(steel manufacturing) is a major source of Volatile organic compound (VOC), and NOx and emissions [41]. These factors resulted in the low scores on all of the residues. The solar unit received lower scores than the other alternatives in terms of material selection due to the fact that Borosilicate glass used for the evacuated tube collector contains 13% Boron Oxide (B2O3)[42].

Manufacturing[edit | edit source]

In case of manufacturing, all the alternatives received the same score. This is again due to the similar material usage (i.e Aluminum, steel) and the tooling similarity. Aluminum sheets for casing are manufactured from recycled scraps or virgin material.Most solid residues are recyclable except for few additives. Small amounts of VOCs,and NOx emission accompany HDPE pipe manufacturing [41]. For solar unit, glass making produces waste particulates that can contain Lead and Arsenic [43].Also, glass making produces liquid residues during forming processes, and produces Sulfur Oxide and Nitrogen Oxide emissions [43].

Distribution and Packaging[edit | edit source]

In all cases the packaging of the product does not require any material from virgin sources or restricted supply. The installation and shipping of the products has no solid residues besides the packaging boxes, which can be recycled. Also, the use of oils, solvents and water has been minimized within the shipping and installation. No gases are used during installation, though gaseous emissions do occur from shipping, but these cannot be further minimized.

Use[edit | edit source]

During the use of the product life cycle it can be seen from the SLCA that the solar unit receives the highest score. Evacuated tube collectors(solar) are designed to minimize heat loss and are well insulated so that they can work well in colder temperatures [44].The natural gas furnace and air conditioner receives the lowest score because the refrigerant used for air conditioning is CFC, one of the main contributors of ozone layer depletion by breaking stratospheric ozone molecules [45].

Disposal,Recycling[edit | edit source]

The disposal of all the products involves no toxic material and material diversity is minimized, but not all parts are recyclable. The evacuated solar collector received the highest score due to less energy requirement. Most modern geothermal heat pump units are made compact and thus occur as singular bulky units.So, disassembly and transport to a recycling plant requires professional help.In the case of gas furnace and air conditioners, most likely part to be recycled are the Aluminum, steel and other metals parts for which disassembly and recycling is highly energy demanding.

Economic Input-Output LCA[edit | edit source]

Economic Input-Output LCA (EIOLCA) is a comprehensive analysis tool that includes the indirect supply chain inputs and covers a wide range of environmental impacts. Its main advantages arise from its ability to be performed quickly and at relatively low costs.

Natural gas heating & Electric Air Conditioning[edit | edit source]

Gas & Air Conditioning EIO Analysis

For our analysis we have considered a life span of 20 years for the heating and cooling system. The capital cost of both the systems is a onetime cost and is thus considered. The total operational cost is multiplied by 20 to get the overall lifetime cost. Total Dollar value amounts to $44850 CAD or $36132.93USD. Inflation adjusted 1997 US dollar amount i.e. $26935 USD[46]is inputted into the EIOLCA tool [47].

The figures on right outline the key features from greenhouse gas emission; toxic releases and energy usage information achieved using the Economic Input-Output Life Cycle Assessment model.

Most of the greenhouse gas emissions come from ferroalloy and related product manufacturing with forced air heating sector and iron and steel mills section being other major greenhouse gas emission sectors. Power generation causes the most toxic releases at 29% followed by iron and steel mills and waste management serves at 12% and 7% respectively.Power generation and supply also uses the most amount of energy at 30% followed by iron mills and AC, refrigeration and forced heating contribution towards 13% and 9% of the total energy use.

Geothermal heat pumps[edit | edit source]

Geothermal Heat Pump EIO Analysis

EIO analysis is divided for two components: HDPE Pipe, GHP and water pump unit. The input costs are inflation [48] and currency adjusted (in US dollars) and are as follows: HDPE Pipe: $633, GHP & Water pump: $11338

Environmental Impacts with regard to Geothermal Heat Pump Manufacture come mostly from Green house gases and Toxic Releases. With regards to GHG emissions, CO2 is the biggest culprit accounting for 80% of the GWP measure. Among Toxic releases, Land releases in form of toxic solid waste account for 76% of all toxic release. A single unit of GHP manufacture requires 0.088 TJ of energy with 70% of the energy being accounted in the form of Coal & Natural Gas. Environmental Impacts regards to HDPE pipe [0.1m (diameter), 190m (length)] and fittings manufacture once again come mostly from GHG and toxic releases. CO2 accounts 85% of the total GWP measure and land toxic releases account for 80% of the total toxic releases. Total energy required for manufacture of HDPE pipe of given length and plastic fittings, is 0.009 TJ.

Evacuated solar collectors[edit | edit source]

Evacuated Solar Collectors EIO Analysis

Inflation and Currency adjusted value of $11,935.99 [49] is inputted into the EIOLCA tool.

The top three greenhouse gas emitters and Power generation and supply, Iron and steel mills and waste management and remediation services at 33%, 19% and 17% respectively.

The top toxic releasing sectors are gold, silver, and other metal ore mining, alumina refining and primary aluminum production respectively.

The top three energy intensive sectors are power generation, alumina refining and other nonmetallic mineral mining at 23%, 21% and 14% respectively.

The total greenhouse gas emissions from natural gas furnaces and electric air conditioners, geothermal heat pumps and evacuated tube collectors are 36.426, 32.819 and 31.456 MT of CO2 equivalent respectively. The total toxic emissions from natural gas furnaces and electric air conditioners, geothermal heat pumps and evacuated solar collectors are 186.18kg, 78.391kg and 50.68kg respectively. Lastly, the total energy usage for natural gas furnaces and electric air conditioners, geothermal heat pumps and evacuated solar collectors are 0.418 TJ, 0.088TJ and 0.0.785TJ respectively.

We notice that evacuated solar collectors have advantage over other alternatives in all 3 categories examined. Therefore, we can conclude that evacuated solar collector is the best alternative for home heating and cooling according to Economic Input-Output Life Cycle Analysis.

Societal Analysis[edit | edit source]

There are some societal issues associated with all the different options of residential heating and cooling.It is noticed that the issues concerned with evacuated solar collectors are minor compared to natural gas heating and electric cooling and geothermal heat pump systems. Heat collectors offer a flexible alternative to prospective buyers looking to augment their current system (natural gas and electric air conditioner) with a more environmentally friendly alternative and not necessarily looking to make a radical shift in their energy usage habits. Also, noise is not an issue for the tube collectors as in the case of electric air conditioners due to the moving fan.

Natural gas heating & Electric Air Conditioning[edit | edit source]

Even though natural gas is the cleanest of fossil fuels during the production process, it does cause some issues that adversely affect the environment. It is likely that the construction and operation of a liquefaction plant creates noise and thus disturbs nearby humans and animals. Constant noise exposure can cause several disturbances in human life such as: sleep interference, communication difficulties, effects on the performance and behaviour of students, and a feeling of annoyance that undermines quality of life [50] .Construction of pipelines that cross Aboriginal land is one of the most controversial aspects of the social and economic consequences. The pipeline right-of-way (15 m to 25 m wide), has an impact on the biotic components of the environment, and on agricultural and forestry activities [50]. The primary method of Electricity generation in Ontario is Nuclear power plants. Nuclear plants relying upon water for cooling requires two-and-a-half times as much water as fossil fuel plants, thus having huge impact on aquatic habitat and water resources [51]

Geothermal heat pumps[edit | edit source]

Retrofitting just for the sake of being environmentally responsible presents a headache for the consumers as the Ductwork would also require reinstallation. Homeowners would soon realize retrofitting to be a money sinking operation and over the long run, it would be impossible to recover the total cost of the new system through lower energy bills. As such, it is advised to have geothermal units installed only in houses undergoing construction or major renovation.Provincial and Federal Governments provide several grants and incentives to homeowners who conduct energy saving retrofits or chose energy saving systems in houses under construction [52] .However, still the potential market is limited to those who can afford to buy and install such a system on their existing homes. Homeowners, however, will tolerate this if other factors such as comfort and environmental benefits can be clearly demonstrated.

Evacuated solar collectors[edit | edit source]

The evacuated tube collectors have to be mounted outside the building, whether on the roof or on the side of the building and the aesthetic appeal may be a point of dispute. Having a large array fixed to a home may not be appealing to some people and may discourage them from purchasing an evacuated tube collector. When compared with natural gas and electricity, evacuated tube solar collectors produce little noise and no physical affects from its operation.The tubes are insulated to decrease the amount of heat lost due to lower ambient temperatures, but this also allows for snow to build up on top of the evacuated tubes since there is no escaping heat to melt it [53]. Clearing the snow is also an issue since the glass tubes are fragile. [53].

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