The effect of greenhouse vegetation coverage and area on the performance of an earth-to-air heat exchanger for heating and cooling modes

Figures & data

Figure 1 Schematic of an EAHE (Ozgener and Ozgener 2010).

Table 1 Climate data for the Mashhad region.

Month	Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.	Year
Recorded high (°C)	24	26	32	35.4	39.2	41.6	43.8	42.4	42	35.8	29.4	28.2	43.8
Average high (°C)	7.2	9.2	13.9	20.8	26.6	32.2	34.4	33	28.9	22.3	15.4	9.7	21.1
Average low (°C)	–3.8	–2.1	2.6	8.2	12.2	16.2	18.5	16.2	11.5	6.1	1.7	–1.9	7.1
Recorded low (°C)	–27	–28	–13	–7	–1	4	10	5	–1	–8	–16	–25	–28
Precipitation (mm)	33	35.2	55.6	46.3	27.6	4.2	1.1	0.8	1.7	8.6	15..4	24.7	255.2
Sunshine (h)	149.1	147.3	161.2	198.6	279.2	341.7	366.1	358.7	304.5	247.4	187.5	15.1	2892.4

Figure 2 Metal frame with 100% vegetation coverage and the EAHE with inlets and outlets (1) and a greenhouse covered with plastic material (2).

Figure 3 Temperature changes in the cooling mode during the day: soil (T_s), inlet (T_i) and outlet (T_o) temperatures of the EAHE.

Figure 4 Temperature differences between the control and treatment greenhouse units at the different levels of floor area and vegetation coverage in the cooling mode: (a) with no (zero) vegetation coverage, (b) 50% vegetation coverage and (c) 100% vegetation coverage.

Figure 5 Soil (T_s) and ambient (T_a) temperatures.

Figure 6 Temperature differences between the control and treatment greenhouse units in the heating mode: (a) with no (zero) vegetation coverage, (b) 50% vegetation coverage and (c) 100% vegetation coverage.

Table 2 Summary of the temperature differences for the heating and cooling modes (mean square).

		Cooling			Heating
Source	DF	9–11	12–14	15–17	18–24	2–6
Greenhouse floor area (S)	2	5.266**	20.523**	5.541**	0.408**	1.557**
Vegetation coverage (D)	2	14.799**	12.739**	10.634**	2.670**	3.745**
S × D	4	0.252**	1.025**	0.67**	0.001 (NS)	0.016*
Error	18	0.29	0.26	0.051	0.004	0.004

Note: NS, not significant; *, significant at the 5% level; **, significant at the 1% level.

Table 3 Heat transfer rate and COP of the different treatments of the EAHE system.

	Heat transfer (kJ/h)		Coefficient of performance of EAHE (COP)
Treatment	Heating mode	Cooling mode	Heating mode	Cooling mode
D1S1	1502.2	4976.9	1.01	3.35
D1S2	1448.5	5094.4	0.98	3.43
D1S3	1448.5	5417	0.98	3.65
D2S1	1316.8	5094.5	0.89	3.43
D2S2	1370.5	5500.3	0.92	3.70
D2S3	1360.7	5626.6	0.92	3.52
D3S1	1185.1	5534.5	0.80	3.73
D3S2	1243.7	5921.4	0.85	3.98
D3S3	1268.1	6413	0.85	4.32

Ozgener, L., and O.Ozgener. 2010. “An Experimental Study of the Exergetic Performance of an Underground Air Tunnel System for Greenhouse Cooling.” Journal of Renewable Energy35: 2804–2811. 10.1016/j.renene.2010.04.038.

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