Table 15. Monthly Average Temperatures for Worcester

As we can see the average low temperature is in January and it is about 17 F. A very good practice in
designing systems is to take in account and to calculate the worst case scenario in order to promote a
more efficient system. For this reason in all the heating calculation we used the lowest average
temperature taken from the tables above.

Another important aspect that we will need to determine is the exposed surface area of the
greenhouse. That’s where the heat is going to escape. To calculate the surface area we have to design a
rough design of the greenhouse with exact dimensions. After that we use the calculations in appendix A
to determine the total surface area. A design sample if shown in the diagram nr 1.

From the calculation we see that we have a total exposed surface area of: 1760 sq. ft.

The next part of the equation for the heat is the heat loss coefficient of the material used. In our design
we choose Solexx as the best material. It is a very good insulator with thermal coefficient of 0.45 and is
widely used amount greenhouse builders. From the calculation (Appendix B) the total energy required
to maintain the temperature at 60F is about 36185 29686 BTU or 10.6 01 KWH for the lowest average
temp yearly.

We also have assumed that the heating is going to get generated by electrical energy so the cost is
going to be calculated in price per kWh, currently in city of Worcester. After considering all this factors
and using the formulas in Appendix C we have the highest possible costs shown in table 2 1. This is a high
estimate and could be reduced by lowering the target temperature inside the greenhouse in the winter
months.

JAN FEB MAR APR MAY JUN JUL

Y

AU

G

SEP OCT NOV DEC Year

Temp. 17 19 26 37 47 56 62 60 53 42 33 23 39.583

33

kWh 3259 3142 2536 1765 955 265 0 0 478 1345 2042 2745 1544.3

33

Cost 554.03 534.1

4

431.12 300.05 162.35 45.05 0 0 81.2

6

228.6

5

347.1

4

466.

65

262.53

67

Cost with

Sundays

397.05

48

400.6

05

316.15

47

220.03

67

119.05

67

32.285

83

0 0 56.8

82

160.0

55

260.3

55

342.

21

189.24
52
*Assuming 0.17ct/kWh
**Assuming the temperature is at lowest average all month
Table 16. Estimated Monthly Heating Costs

As a conclusion see that the cost is relatively high in the winter months. So in order to run throughout
the winter we would need efficient heaters to ensure a minimum temperature. Also to reduce the costs
we need other methods of insulation. So to compensate the 8.668 kWh loss we will need an electrical
heater or combined heaters that will have rating of at least 9 kWh, where we have to include their
efficiency that is not 100 %.The recommendation we identified 2 heaters that could fit our solution, the
King Pic-a-Watt 240v Electric Heater, providing 5.7 kW for $399, and the Dayton U36 240v Electric
Heater, providing 5.6 kW for $179.