Hotel Perote solar pool heating system

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Background

Parras de la Fuente

Parras de la Fuente is a desert oasis town of about 44,000 residents located in the south of the Mexican state of Coahuila. Along with textile manufacturing, tourism is one of the main industries in Parras. Tourism has become increasingly emphasized after Parras's designation as the "primer pueblo mágico del Norte de México." Parras is warm in the summer, and cooler in the winter, but temperatures rarely fall below freezing, snow falls once every several years.

Elevation
1,505 m
Longitude
102°11'W
Latitude
25o30’ N

Hotel Perote

Hotel Perote, or Antiqua Hacienda de Perote, is a hotel, restaurant, 500 acre nuez (walnut) ranch and vineyard, and winery. It is located on the western-most edge of Parras. According to Igancio (Nacho) Chacon, Perote's owner, Perote's hotel business has been growing rapidly, and in 2006, the hotel was adding rooms to meet demand.

Contacting Hotel Perote

Visit Hotel Perote's in-town office, near UTC Parras
Ramos Arizpe # 131 Col. Centro C.P. 27980
Parras de la Fuente, Coahuila
Call the Hotel Perote in-town office (see Phone Calls section of Parras Handbook)
(842) 422 1698
Fax
(842) 422 0698
Call Lic. Ignacio Chacon's (owner's) mobile phone
Email Aaron Antrim to get this phone number
Website
Antiqua Hacienda de Perote

Visiting Hotel Perote

Go a few kilometers west on Calle Madero, the street in front of UTC Parras, passing turns for Estanque de la Luz and La Illusion. Consult this map from the Hotel Perote website for additional directions. A cab to Perote from UTC will cost 50 pesos. See the Taxis section of the Parras Handbook for more information.

2005 History

Parras Program students Heather Kuoppamaki and Rowan Steele built a rooftop solar hot water system for Hotel Perote in the summer of 2005. Intended as prototype for a larger system to heat a spring-fed swimming pool (alberca), then being constructed, the system was sized to provide heated water for a single hotel bathroom. For more information on the 2005 system, Heather and Rowan's final document for their system. The 2005 system is no longer located at Perote, and has been moved to the residence of someone afiliated with the local city government. For more on the whereabouts of this system, contact Ignacio Chacon.

2006 Alberca Heating System Design Proposal

PeroteAlberca.jpg

Facts

Currently, two pool pumps circulate water through a sand filtration system. The roof of the building on which the solar system will be installed has a height of 26 feet. While the space available on the roof has not been measured from the rooftop, the interior area beneath the roof has been used to estimate the space available for the solar collector. The interior area dimensions are 77 ft by 31 feet. Igancio has requested that the pool be kept at 28 degrees centigrade from October to March.

• Pool surface area

(11.2 by 6.7 meters)+(1.82*pi) = 85 square meters

• Pool volume


The total volume of the pool is approx 112 cubic meters, or 112,000 liters.


System design

SHWH collector diagram.png

The system will have a collector consisting of thirty runs of half inch copper pipe, each three meters in length. One and a half inch schedule forty PVC pipes will carry the water to and from the roof. The lengths of half inch copper pipe will be connected to the one and a half inch PVC pipe by tees. The collector will be connected after the filters and installed on the roof. Since the filters have pumps in them already, additional pumps will not be needed to carry the water up to the roof. In order to increase ease of testing, the system will include a spigot for obtaining water temperature readings at a point after the water has passed through the collector. A thermometer will also be installed in the pool to take temperature readings there.

SHWH collector closeup.png

SHWH valve setup.png


Predicted temperature change in pool

T = (Vc/Fc)(Qp/mc)/(mtsw)

T = change in temperature Vc = volume of collector Fc = flow in collector Qp = heat transfer in pipe (from test) mc = mass of water which passes through collector mt = total mass of water sw = specific heat of water


Qp = mswT

Qp = heat transfer in pipe (from test) m = mass of water in pipe sw = specific heat of water T = change in temperature


Effectiveness of Solar Collector for Perote

The sizing of the collector for the pool system is difficult to determine. In order to maintain the pools temperature throughout the winter it is necessary to determine the energy loss of the pool during that time, something that is difficult to do in July. The system was designed based on the available supply of copper pipe, if this proves to be inadequate the system was constructed in such a way that it is easy to expand and therefore increase the detention time in the collector. At the first meeting at Hotel Perote 100 meters of half-inch copper pipe was made available for this project. This gives the collector a volume of 50.6 liters. The manual for the pumps was not available, and it was not possible to measure the flow before construction, so a estimate of 114 L/m was used for the flow rate. This flow rate was based on US pump sizing standards for the pool volume. Based on the collector volume and flow rate the hydraulic retention time is:

T = V/Q = (50.6 L)/(114 L/m) = 0.44 m

Unfortunately this retention time is rather small and the testes conducted with the copper pipe may not be accurate at this range. The water temperature in the test pipe gained about two degrees (C) per minute for the first couple of minutes in direct sun. Based on that data it was estimated than in the first half minute the temperature will increase one degree. The volume of water being heater was based on the flow rate and the equivalent of a minimum of 4.5 hours direct sun in the winter:

V = T*Q = (4.5 hr * 60 m / 1 hr) * (114 L/m) = 30780 L

To determine the energy added the volume is changed to mass using a density of 1 L/kg, which means that 30780 kg of water is heated 1C.

Q = mswT

Q = heat transfer m = mass of water sw = specific heat of water T = change in temperature

Q = (30780 kg)(4.186 kJ/kg* C)(1C) Q = 128845 kJ ≈ 129 MJ

The addition of 129 MJ per day seems large, however when considering the volume of the pool the effect may not be substantial. The only way to know weather the 129 MJ is enough is to monitor the pool temperature over the course of a year. If more heat needs to be added the collector volume can be increased without much difficulty.

External Links

"Water Heater Efficiency" [1]

"Energy From Natural Gas" [2]