DESIGN OF A LOW CARBON HOME: A RETROFIT CASE -

DESIGN OF A LOW CARBON HOME: A RETROFIT CASE

INTRODUCTION

Definition of low carbon homes: these are homes which have been designed in such a way that they release very little or zero green house gases throughout their lifetime. According to Seyfang, (2010), buildings contribute to about 38% of all the green house gases (GHG) alone. The global temperatures and GHG will continue to increase and if nothing is done up to 2050 we will have those numbers more than doubled. Fuel prices are also estimated to increase by 60% by the year 2020. For a sustainable climate and environment, we will have to make several changes to the way energy is generated and used.

In building, GHGs are released during construction, operation, renovation and demolition. During construction GHGs come from manufacturing of materials, transport of materials, and construction machinery. During operation these gases come from electricity consumption which has been generated from fossil fuels, using gasoline in cooking and water heating or cooling as well as the little of it that come from the use of biomass as an energy source in most parts of Africa. Renovation machineries also release these gases and so are the demolition machineries. The most significant contributor of GHGs in the housing sector is the energy consumed in the house during it economic life or operation (Osmani, 2009).

Low carbon homes have much greater energy efficiency hence reduced energy bills, more productivity from renewable energy as well as an effective climate change mitigation process (Goodall, 2007). There are also various factors which affect the use of energy in the houses or homes which include the behavior of the occupier or owner and also the system inefficiency in energy use. It is through these factors that we design houses which are efficient in energy use and energy saving (Seyfang, 2010).

Objectives

This paper will carry out an upgrade or retrofitting of an existing house to make it a low or zero carbon building so as to reduce its dependence on the fossil fuels. Firstly, design conditions will be specified based on a thorough understanding of the layout and the use of the building. It will carry out calculations of the initial thermal performance using peak cooling load both before as well as after the shading. The risk of overheating will also be assessed by investigating peak temperature at each floor by use of admittance method (Lee, 2009).

The second stage will propose the possible strategies to reduce energy consumption. There are various areas in a house or home which provide opportunities for energy saving. Lighting strategies e.g. use of energy saving bulbs or use of natural light during the day provides one such possibility. Thermal strategies like use of building envelopes, natural ventilation as well as insulations will also be examined. Every solution will be selected based on its effectiveness verses limitations. Integration of renewable energy source will also be considered (Li, 2008).

Background

This project is located in Singapore and it has the following geographical information.

Latitude 1.37 N

Longitude 103.98 E

From the Ecotect website, weather data is downloaded so as to help in analysis.

1.2.1 Description of the building

It is a three floors building with an exhibition centre at the ground floor, a library and cafe at the first floor and an office at the second floor. It has a West – East orientation (for its windows are mostly on East and West) and it is also surrounded by a two other blocks and a playing field. It has glazed windows and doors. Bottom windows are fixed; upper windows are operable (Chua, 2010).

Figure 1-1 West facade

Figure 1-2 East façade

The working hours for each floor is shown in the table below

Ground Floor	Exhibition Centre	10am-10pm
First Floor	Library	10am-9pm
Second Floor	Office	9am-5pm

The dimensions of the building are given in the table below

Building Dimension (m)
Length	54			Framework Ratio For Glazing Area	5%
Width	18
Height	Ground Floor	2.7
	First Floor	2.7
Second Floor	2.75
Area　()	North	East	South	West	Total
Window	0	163.5225	13.77	294.06	471.3525
Wall	190.8	329.03	171.8595	278.34	970.0295
Door	0	79.8475	5.1705	0	85.018
Glazing Area	0	243.37	18.9405	294.06	556.3705
Total	190.8	572.4	190.8	572.4	1526.4

(Turiel, 1985).

1.2.2 Population and capacity

The number of people in ground floor is 297 and 5 computers, while first floor is 127 and 38 computers, 3 printers, 1 café brewer, 1 micro wave, 1 refrigerator and 1 steam kettle. The second floor has 100 people, 54 computers, 3 printers and 3 photocopiers.

1.2.3 Weather data

Climate Condition: Singapore is mainly hot and humid and experiences all year-round showers of rain because it is a tropical rainforest climate. Temperature: almost constant all the year-round with an average of 23 to 32. Relative Humidity: very humid year round with an average of 70% to 90% and 100% during rainy days. Solar Radiation: it is majorly constant with a total of 1635kWh/m2 (Chua, 2010).

PROPOSED DESIGN CONCEPT
- internal conditions

For interior comfort of the occupants, the internal conditions of the building should meet the following criteria by parameters.

Building type	operation temperature	Air supply rate	Maintained luminance
Office	26°C	10l/s/person	500lux
Library	26°C	10l/s/person	300lux
Exhibition Hall	26°C	10l/s/person	200lux

The temperature chosen is 26°C

The air supply rate is 10 liters per second per person at a speed of 0.25m/s

The relative humidity is between 40 -70 % (Tuohy, et al, 2010).

Thermal performance

To analyze thermal performance of the low carbon building, we will need to calculate the peak heat gain. Peak heat gain is a total of peak solar heat gain, the fabric heat gain, the ventilation heat gain and the internal heat gain (Chen, et al, 2011).

peak solar heat gain

From the solar table 5.25 in CIBSE guide A. We have the peak being in February 16:30 and the framework ratio is 0.05 with a correction factor of 0.92. Assuming that the building is with clear glazing and heavy thermal mass, then the peak cooling load is given as follows.

Internal heat gain

Internal heat gain will be = people heat gain + equipment heat gain.

Heat gain per person in office or library = sensible heat + latent heat = 75+55=130W/person (Chen, et al, 2011).

Sensible heat gain for lighting is given as 6, 11 and 12 W/m²for ground, first and second floor respectively and for the equipment is 3W/m^2.

Therefore, total heat gain per floor will be given as Ground floor = 44074W

First floor = 36139W, and Third floor = 33874W

Total internal heat gain = 44074+36139+33874 = 114087W ≈ 114kW

Ventilation heat gain

The outside peak temperature is taken as 32 ⁰C and the design room temperature is taken to be 26 ⁰C. Heat gain Q is given by Q = cV (T_out – T_design).

, , () but fresh air flow rate = 10l/s/person and there are 524 people hence v=5.24m³/s

Therefore

Fabric heat gain

This is given by

From the data given the fabric heat gain is given by

Category	U value (W/m²C)	Area (m²)	ΔT (°C)	Q (KW)
Wall	3.15	970.03	6	18.34
Roof	1.29	972	6	7.52
Glazing Area	5.1	556.37	6	17.02
Total				42.89

Thermal performance or the total peak heat gain is given as follows

Solar Heat Gain (KW)

Internal Heat Gain (KW)

Ventilation Heat Gain (KW)

Fabric Heat Gain (KW)

Total Heat Gain

(KW)

177

114

40.76

42.9

374.66

47.24%

30.43%

10.88%

11.45%

100%

Peak internal temperature

The maximum internal environment temperature should never exceed the allowable comfortable range.

The mean heat gain through glazing is given by
Mean casual gain

Ground Floor	Exhibition Centre	10am-10pm	44.07KW
First Floor	Library	10am-9pm	36.14KW
Second Floor	Office	9am-5pm	33.87KW

To calculate mean casual gain we need to calculate Q_cas shown in the figure above.

Then mean casual gain will be worked out as Q_cx t/24

Proposed modifications

To improve the thermal comfort of the building the following has to be done.

Reduction of the glazing area

Reduce the height of some of the windows even to about half the size of the initial building. Also convert most of the glazed doors to opaque ones to reduce the glazing area by the size of that door (Lampert, 1998).

Improvement on the construction materials

Since this is a retrofit, one can only change a few of the construction materials and not the whole shell; else it will be a rebuilding afresh. So the wall cannot be changed but we can make use of the glazing and modify the material for glazing. Use a double glazed material with low values of E, U and Y so that it will increase the reflecting ability of the material and decreases the conduction ability of that radiation into the building (Venkatarama, 2003).

The main disadvantage with these two modifications is that, there is a reduction in visible transmittance hence less daylight enters the building and this in turn increase the requirement of artificial lighting (Lynes, 1968).

Installation of the windows shading devices.

This is the use of inside blinds or inside curtains and also the use of outside automated shading devices with a horizontal plane which will always be perpendicular to the sun light rays. They should be mostly installed in the West side which has large glazing area and the strongest solar radiation that occasion during peak time. The width of the shades should be 0.3M for both ground and first floor and 0.6M for second floor (Shaviv, 1999).

Analyzing the modified building

The modified specifications are now analyzed to compare with the initial building to see the effect of such improvements. We will evaluate its thermal performance.

The calculations, done in the same manner as before yield these results for the new design.

The new peak solar heat gain = 34.46 kW

The new fabric heat gain = 33.32kW

The internal heat gain = 114 kW (No change)

The ventilation heat gain = 40.76 kW (No change)

The total peak heat gain = 222.54kW down from 374.66kW

Solar Heat Gain (KW)	Internal Heat Gain (KW)	Ventilation Heat Gain (KW)	Fabric Heat Gain (KW)	Peak Heat Gain(KW)
34.46	114	40.76	33.32	222.54
15.48%	51.23%	18.32%	14.97%	100%

The biggest contributor of this peak heat gain here is internal heat gain which is different from the first scenario where much of it was from solar heat gain.

The new peak internal temperature gives the following outcomes

Peak Temperature ()	Initial Building	Designed Building
Ground Floor	45.68	43.37
First Floor	46.32	43.89
Second Floor	45.90	43.23

The peak temperature do not change much and are still beyond comfortable range, which means that in this part of the world, the room temperatures cannot be corrected by a passive means but a mechanical method is applicable to keep the temperatures in their acceptable range.

Ventilation

This is a very important part of the building so as to achieve thermal comfort. It is basically a method that is commonly used to cool a building by driving out much of the internal heat energy of a building and then replacing it with more fresh air from outside the building. There are various ways in which one can achieve ventilation. These includes the natural ventilation method which has no much influence from human work, there is also the mechanical method which is artificial and there may be also a combination of the two methods which is a mixed method of natural and mechanical method (Shaviv, 1999).

Design scenario

This part will design an effective and efficient ventilation system for Singapore Low Carbon building.

Climate specifications

Singapore prevailing climatic condition is a tropical one. This means that the country will remain to a constant of hot and humid all the year round. However, this area receives some considerable amount of rainfall at some time of the year despite the fact that there is no distinct dry or wet season. This is as a result of the disparate monsoons that affect the region. The temperatures can at times reach a maximum of 32.3 ⁰C on a very hot day and the humidity levels are always ranging between 70% to 80%.

Design criteria

In order that the design engineer puts up a ventilation system, he must meet the following two vital requirements.

Supply of the fresh air for all the occupants of the building
Sufficiently change the air inside the building so that hot air, fumes, smells as well as the contaminants are taken out of the building (Shaviv, 1999).
- Calculating fresh air requirements

Ground floor: exhibition

There are 297 occupants on the ground floor. According to the CIBSE guide A, there is a fresh air flow rate of 10l/s/person for maximum comfort. Thus, the whole first floor will require 297 x 10 /1000 = 2.97m³/s

Air change rate (ACH) = flow rate x 3600/volume. Volume = 54 x 18 x 2.7 = 2624.4m³

Therefore, ACH = 2.97 x 3600/2624.4 = 4.07

First floor: library

Occupancy: 127

The specified flow rate is 10l/s/person as above and so will it be for an office as well in second floor

Therefore flow of fresh air required = 1.27 m³/s

Hence ACH = 1.174

Second floor: offices

Occupancy: 100

Fresh air required = 1.0 m³/s

ACH = 1.35

With this information one can therefore gauge the possibility of using either natural ventilation, mechanical ventilation or a mixed mode ventilation and compare the figures to see which the most viable method is.

SYSTEM INTEGRATION: HVAC CONSIDERATION

Energy star certified systems are recommended because they have passed the energy saving inspection. The system should have adequate controls to allow shut down by occupants. They should have the newest technology design for energy conservation. The main advantage of these HVAC systems is that they help in maintaining the occupants’ comfort as constant as possible (Canbay, 2004).

Use of natural light

This is the most efficient source of light than any artificial source that has ever existed. It is more pleasant and superior than any other. The following table shows daylight factors (DF) for every floor before redesigning. It shows that 1^st and 2^nd floors have very little DFs hence they need redesign.

Floor	Daylight Factor
Ground floor	5.8%
1^st floor	0.9%
2^nd floor	0.9%

After modification and considering the issue of shading, the new results are as follows

Floor	Daylight Factor*
1^st floor	7.5%
2^nd floor	1.8%
3^rd floor	3.4%

This shows that the DF has improved significantly, hence reducing the need for artificial lighting and saving energy.

Renewable energy incorporation

The renewable energy sources put into consideration here are solar, wind and biogas. After evaluation solar is the most appropriate since it has no much side effects and also its versatility in that it can be used as solar thermal and solar photovoltaic.

Solar photovoltaic is incorporated in this building to provide electricity necessary for running the computers and HVAC systems and other electronics installed. Its justification is shown below (Johansson, 1993).

Active solar radiation has approximately 2.4kWh/M²day of energy with an efficiency of 25%. Therefore the roof area 54m x 21m will yield an output of 680 kWh of power in 10 hours a day. This is large enough to run many of the electronics and machines in the building (Bakas, 2011).

Wind energy is not recommended because of its cut in speed for turbines which is generally 5-7 m/s but in this region the speed is 2-3m/s. Biogas not recommended also because it requires continuous supply of effluent which may not necessarily be there. It is mainly applied in heating which is not also necessary in this building. So it is not feasible (Johansson, 1993).

Solar energy remains to be the best option for this building and its sustainability.

ENVIRONMENTAL AND ECONOMIC BENEFITS OF THE DESIGN
- Environmental benefits

Some of the environmental benefits include:

Thermal comfort of the workers
In door air quality
Safety of the occupants
Climate change mitigation
- Economic benefits
Productivity of the workers due to comfort
High equipment life before of the operating conditions
Low or nil energy bills hence, change order or warrant claims due to reduced production cost.
Short time payback period of the retrofit which is mostly 3 years and below (Seyfang, 2010).
CONCLUSION

This project was aimed at lowering or minimizing the GHG emissions from this building by reducing the amount of energy required to run various. So far, we have utilized energy saving opportunities at our disposal to retrofit this house to the maximum energy saving possible. The areas we have improved on this building include:

thermal performance

We calculated the peak heat gain and the peak temperatures to see how we can put strategies to ensure maximum thermal comfort. We had to deal with solar heat gain which was the biggest contributor to the total heat gain with approximately 47%. We reduced the glazing and also introduced shading effects and this reduced the energy requirement by far. The problem now was how to reduce the internal heat gain which was now 51% contributor to total heat gain. That is why we introduced the issue of HVAC, which consumes energy but now we need to have a source of renewable energy as discussed below (Canbay, 2004).

Ventilation

We also had to deal with the flow of air in the building and designed a system that meets maximum comfort of the occupants by use of mixed mode of air circulation (Shaviv, 1999).

Day light

We also had to reduce the artificial lighting requirement hence reducing the energy required to light the building. We had to to make good use of the natural light from the sun (Lynes, 1968).

Renewable energy

We also needed to have a renewable source of energy to sustain the energy required to run the electronics and the HVAC installed. The most favorable source was solar photovoltaic which could meet approximately 65% of the total energy requirement hence reducing fossil based emissions by far (Johansson, 1993)

The building has now been retrofitted to a low carbon building.

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