Solar Updraft Tower Using Compost Waste Heat and Transpired Solar Collectors

K. R. Anderson*, A. Ang*, R. Osorio*, and A. Villanueva*

*California State Polytechnic University, Mechanical Engineering

Solar Thermal Alternative Renewable Energy Lab, Pomona, CA, USA,

kranderson@cpp.edu, asang@cpp.edu,rfosorio@cpp.edu,evillanueva@cpp.edu

ABSTRACT

This paper explores the use of ways to enhance energy

production capability in Solar Updraft Towers (SUT) by

using Compost Waste Heat (CWH) and Transpired Solar

Collector (TSC) renewable energy technologies in unison.

The current research presents experimental and numerical

modeling results for the SUT CWH greenhouse walls

constructed from TSC materials. The paper includes the

results obtained for the power production from a 1/5th sized

scaled model of a SUT using CWH and TSC in unison.

Numerical heat transfer simualtions are also presented

showing the effect of greenhouse roof tilt angle and inlet

tower air velocity on the overall heat transfer coefficent of

the SUT system.

Keywords: solar chimney, composting, waste heat,

transpired collector

1 INTRODUCTION

The SUT is also referred to in the literature as a Solar

Chimney, in which turbines located at the base of a large

chimney mounted on the roof of a solar greenhouse are

used to produce electricity via the natural convection

updraft set up by the solar chimney which causes a wind

velocity on the order of 9 mph (4 m/s) to spin a series of

shrouded turbine blades to produce power. Figure 1 shows

the configuration being studied herein.

SUT

TSC WALLSCWH GREENHOUSE

Figure 1: Solar updraft tower with compost waste heat

removal and transpired collector walls.

Figure 1 shows the SUT chimney tower, which has a tubine

located at its base, the CWH greenhouse building used to

house the composting waste heat harvesting portion of the

technology, and the TSC walls which are used to fabricate

the walls of the CWH greenhouse. The concept of using the

SUT with CWH has been published by our research team in

previous studies including [1-2], whereby the civil

engineering design of a compost waste heat to energy solar

chimney power plant and it’s assocaited economic

advantages is given. In the study of [3] a comprehensice

thermal-fluids analysis of a hybrid solar/compost waste heat

updraft tower is presented. In the work of [4] CFD analysis

of hybrid solar tower using compost waste heat and

photovoltaics is presented. The review of solar updraft

tower power generation given by [5] notes the current SUT

CWH research of our team as being novel and innovative.

The recent study of [6] provides a case study of energy

recovery from commercial-scale composting. The current

paper extends the propostition of using SUT CWH with

TSC first gvien by [7]. The concept of using TSC walls

with an SUT and CWH is illustrated in Figure 2.

ROOF OF CWHGREENHOUSE

TSC WALL

FRESHAIR

HEATED AIR FROM TSC

GROUND FLOOR

COMPOST PILE

CHIMNEY WALL

SHROUDED TURBINE

HEATED AIR FROM CWH

Figure 2: Use of TSC walls for the greenhouse walls of

the SUT CWH power plant.

As shown in Figure 2, the TSC walls are used in unison

with the SUT and CWH to augment the convective flow fed

into the power turbine of the SUT CWH TSC power plant.

The merits of using the TSC in conjunction with a SUT

employing CWH were first introduced in [7]. In the case

study of [8] a 2 CFM TSC system with solar radiation of

500 W/m2 is seen to give a T = 20 C of temperatue

21Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2018

potentail. This amount of temperature differential is directly

proporation to an increase in heat transfer coefficient

(HTC) per

bh a T (1)

as discussed in [7].

2 NUMERICAL MODELING

A numerical Computational Fluid Dynamics (CFD)

Heat Transfer model was constructed to predict the

behaivor of a particular SUT due to changes in the HTC, h

slope of the roof, velocity of inlet air into chimney, V, etc.

Figure 3 shows axisymmtric model used, while Figure 4

shows a zoomed in view of the the mesh used for the

numerical CFD model.

TSC

SUT C

HIM

NEY

TURBINEINLET

Figure 3: Numerical heat transfer model mesh of of SUT

with CWH and TSC.

Figure 4: Zoomed in view of numerical heat transfer model

mesh of SUT with CWH and TSC.

The numerial simulations were performed with ANSYS

FLUENT CFD Numerical Heat Trasnsfer software. Typical

results of the numerical analysis are shown in Figure 5.

Figure 5: Numerical heat transfer simulation results for

effect of SUT greenhouse roof slope , on tower entrance

temperature, To and HTC.

Results from the numerical heat transfer model show that

the heat transfer coefficient (HTC) varies from 15 < h < 25

W/m2-K depending on wheter the side walls of the CWH

greenhouse are fabricated out of plain walls, h = 15 W/m2-

K, or TSC type walls h = 25 W/m2-K. For the generic

trends it is found that composting addition always results in

more heat and therefore higher temperatures. The non-

compost configuration shows a modest increase in

temperature in all cases as the HTC increases. Regarding

the slope of the roof, as the roof was sloped, some roof

angles show increase in temperature with increased HTC,

while other roof angles show flat or decreasing temperature

with increased HTC. This phenomena is believed to the fact

that addition of compost causes reduced buoyancy driven

flow in the base of the SUT at some angles. In summary,

taller towers causes increased velocity and angled roof

CWH greenhouse maximizes the tower velocity by

reducing flow resistance into the tower. Additional parasitic

heat sources mostly contribute to increasing the air

temperature into the tower with minor effects on increasing

velocity.

3 PROTOTYPE EXPERIMENT

Figure 6 shows the experimental prototype built at

California State Polytechnic University at Pomona.

HOLES USED TO MIMIC TSC EFFECT

Figure 6: Prototype 1/5th scale of SUT with CWH and TSC.

22 TechConnect Briefs 2018, TechConnect.org, ISBN 978-0-9988782-3-2

Figure 6 shows the 1/5th scale prototype of the SUT CWH

TSC power plant with details of the SUT greenhouse

sidewall construction, foam insulation, and structure

comprising the prototype. The following equation from [9]

relates the power output of the SUT to the temperature drop

across the chimney, T and the height of the tower, h are

used to reduce the data

2

o

p

TP c KA T gh

T

(2)

while the prototype power is related to the actual power via

the similarity relationships of fluid mechanics and

turbomachinery [10]

3 5 3 5

prototype actual

P P

D D

(3)

The relationships of (2) and (3) are used to compare the

performance the prototype to actual SUT CWH TSC

powerplant. Preliminary findings are shown in Figure 7.

*

*

*

**

*

* P CWH+TSC prototype (MW)

P TSC CWH prototype (MW)

Figure 7: Comparison of prototype to actual power plant

power output predictions.

REFERENCES

[1] K.R. Anderson, Y. Salem, S. Shihadeh, P. Perez, B.

Kampen, S. Jouhar, S. Bahrani, and K. Wang,

“Design of a compost waste heat to energy solar

chimney power plant,” Journal of Civil Engr.

Research, Vol. 6, Issue 3, pp. 47-54. 2016

[2] K.R. Anderson, M. Shafahi, S. Shihadeh, P. Perez,

B. Kampen, C. McNamara, R. Baghaei Lakeh, A.

Sharbat, and M. Palomo, “Case study of a solar

tower/compost waste-to-energy test facility,”

Journal of Solid Waste Technology & Management,

Vol. 42, pp. 698-708, 2016.

[3] K.R. Anderson, M. Shafahi, and C. McNamara,

“Thermal-fluids analysis of a hybrid solar/compost

waste heat updraft tower,” Journal of Clean Energy

Technologies, Vol. 4 No. 3., pp. 213-220, 2016.

[4] K.R. Anderson, M. Shafahi, R. Baghaei Lakeh, S.

Monemi and C. McNamara, “CFD analysis of

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photovoltaics,” Proceedings of the IEEE SUSTECH

2015 Conference on Technologies and

Sustainability, Ogden, Utah, USA, 2015.

[5] X. Zhou and X. Yangyang, "Solar updraft tower

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125, 2016.

[6] M. Smith and J. Aber, "Energy recovery from

commercial-scale composting as a novel waste

management strategy," Applied Energy, Vol. 211

pp. 194-199, 2018.

[7] K.R. Anderson, “Analysis of SUT using Compost

Waste Heat and TSC,” proceedings of ASES

SOLAR 2017 Conference, Denver CO, Oct. 9-12,

2017.

[8] http://solarwall.com/en/home.php, last accessed

3/23/18

[9] J. Schlaich, R. Bergermann, W. Schiel and G.

Weinrebe, “Design of commercial solar tower

systems–utilization of solar induced convective

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[10] Potter and Wiggert “Mechanics of Fluids,” 3rd. Ed.,

Prentice-Hall, 2002.

23Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2018