Solar hot water system for a hotel in Parras de la Fuente, Mexico

A passive solar heating system was designed, built and installed on the roof of Hotel Perote in Parras de la Fuente to heat the hotel's pool. This design utilizes PVC and copper piping to heat the pool water to 28 degrees centigrade from October to March.

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.

1,505 m
102°11' W
25°30' N


Hotel Perote[edit | edit source]

Antiqua Hacienda de Perote is a hotel, restaurant, nuez (pecan) ranch, vineyard, and winery. It sits on about 500 acres 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 constructing rooms to meet demand.

Contacting Hotel Perote[edit | edit source]

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
(842) 422 0698
Call Lic. Ignacio Chacon's (owner's) mobile phone
Email Aaron Antrim to get this phone number
Antiqua Hacienda de Perote

Visiting Hotel Perote[edit | edit source]

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[edit | edit source]

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, consult Heather and Rowan's File:2005Perotepaper.doc. 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 Project[edit | edit source]

Required system performance[edit | edit source]

Igancio has requested a system to keep the pool at 28° centigrade from October to March. The design problem revolves on this performance parameter and several state variables.

Existing site, equipment, and state variables[edit | edit source]

Pool dimensions[edit | edit source]

Perote alberca dimensions.png

Pool surface area
(Necessary for considering heat loss)
(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.

Installation site dimensions[edit | edit source]

Roof dimensions
77 ft by 31 feet
Roof height from deck
26 feet

Pump specifications[edit | edit source]

The Solar Collector[edit | edit source]

Fig 4: diagram of the collector
The solar collector design calls for 30 three meter lengths of half inch diameter copper pipe run in parallel between two one and a half inch diameter PVC ends. Currently, however, only 20 lengths of copper tube have been installed. The system, however, is easily expandable, and additional copper pieces can be installed by cutting the caps off the ending PVC nipples to add additional T's and reducers. The lengths of half inch copper pipe are connected to the one and a half inch PVC pipe by PVC "T's". For easy testing, the system design requests a spigot for obtaining water temperature readings at a point after the water has passed through the collector, however this feature has not yet been implemented. A thermometer could also be installed in the pool.
Fig 5: close-up of tees

Construction[edit | edit source]

Connection to existing pool plumbing[edit | edit source]

Fig 6: diagram of valve setup

The 2006 project team's design calls for the new rooftop solar collector to be connected to the pipe returning water to the pool after it has passed through the sand filter. Heating water after it has been filtered will prevent debris from clogging the solar hot water heating system. A gate valve can be closed to force water through the solar collector. When open, water will return directly from the filters to the pool without passing through the solar collector.

The pipes to the rooftop solar collector will share identical specifications with the existing pipes running to and from the pool: one and a half inch diameter "schedule 40" PVC. Schedule 40 PVC tubing is thicker than conventional PVC, and is used in pool systems. The additional thickness and strength of schedule 40 PVC will provide improved water pressure tolerance and improved heat and solar radiation tolerance, which will be important, as these PVC pipes will be carrying heated water, and will be exposed to heat and solar radiation on the roof.

The piping delivering and returning water from the rooftop system will first run directly up to the ceiling of the pump room from where it is connected to filter outflow. It will run along the ceiling to the point where it must pass through the concrete floor of the deck above to run 6 meters to the roof.

[calculate head loss for pipes running up to the roof]

Operation[edit | edit source]

  • The main flow control valve (see valve setup diagram, fig. 6) should be opened to allow the water to pass directly to the pool when temperatures may drop below freezing, in order to prevent the pipes from bursting.
  • The collector is only effective when filter pumps pass water through it. Therefore, filter pumps should be run during peak sun hours.
  • Covering the pool at night will increase heat retention.

Effectiveness of Solar Collector for Perote[edit | edit source]

The sizing of the collector for the pool system is difficult to determine. In order to maintain the pool's 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 heated 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 = mswT

  • Q = heat transfer
  • m = mass of water
  • sw = specific heat of water
  • ΔT = 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 whether 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.

Tybie Fitzhugh[edit | edit source]

31 January 2007

When I first arrived, the system was not set up. I asked why, and a technician told me that it was because they did not have a copy of the plans to connect it. Later Ignacio told me that they had needed to change the plans because the system needed an extra ¾ horsepower pump in order to function. He said they had the pump, they knew how to connect it, but that they had been waiting because someone had instructed them to wait until we, the HSU team, gave the new plan the okay. He did not say who it was who had told him that. Later another technician told me that they could not connect the pump because they did not have the plans. I printed a copy of the plans from Appropedia and with Pablo's help, translated it into Spanish and presented the technicians with both the handwritten Spanish translation of the plans and the original English version printed from Appropedia. I tried to talk with the technicians about where to put the extra pump, but that day they seemed to already know where they wanted it. I went up on the roof and took pictures of the pipes – there are still the original 20 lengths of copper tubing.

They actually connected the system, with the extra ¾ horsepower pump, the day before I had to leave. They had told me a few days earlier that I would be able to come and test it. I arrived with the Hobo, but when I went to the basement nothing was running. I asked the technicians if we could test the system and they said they were going to wait to use the system until there was warmer weather. This seemed strange, but they were firm on their decision. There were very few guests staying at Perote. I think in the whole time I saw only three families, all on different days. Most of the time there was no one to be found anywhere in the offices, they seemed low staffed. It definitely seemed off season for business. Most of the time they kept the pumps shut off, and the pool was often dirty. --Tybie

Temperature readings[edit | edit source]

Tybie made readings using a Hobo Data Logger, kindly provided by Lonny.

Note: The logger must be started and stopped by a computer. Since I could not connect the logger to my laptop, Pablo and I started it and stopped it at Pablo's house using his desktop computer. Therefore it was necessary to have the logger running in my backpack for the trip to Hotel Perote and the trip back. This explains for the sudden jolts in temperature at the beginning and end of the logs.

The Hobo Logger has outlets for 4 probes; however, only 3 were connected and activated for testing. Probes 1 and 2 measured ambient air temperature while Probe 3 measured water temperature. In the data logs below each probe has two columns. The first measures degrees Fahrenheit while the second measures degres Celcius. Thus (*F)(*1) is the Fahrenheit column for Probe 1, and so forth. --Tybie

Recommendations for 2007 Team[edit | edit source]

  • Install spigot on the roof to test collector performance.
  • Add additional copper pipe if more heating performance is necessary.
  • Create informational placard to inform guests about the solar hot water system.

2007 Team Update[edit | edit source]

A number of issues prevented our team from making forward progress on the system itself this summer. We did however make progress in identifying the problems and examining other options for Ignacio and Hotel Perote.

Problems/Issues[edit | edit source]

  • Upon examining the system pump and plumbing connections to the pool filtration system, it became obvious that the system was not linked to the pool system as designed by the previous teams. The pump for the solar system is drawing water from the plumbing before it goes through the filtration system. This is bad for the following reasons:
  1. The pump pushing water to the solar system is not a pool pump and does not have a course filter to keep out large objects such as jewelery or other pool originated objects. This could easily destroy the pump;
  2. the small pipes of the solar system are designed for clean water and could become clogged if dirt and debris make their way to the system.
  3. By bypassing the filter system, our system returns dirty water to the pool which defeats the integrity of the filter system, and ultimately it purpose.
  • The pump that was installed to force the water to the solar collector is only strong enough to function for about ten minutes. It quickly becomes overworked and shuts off.
  • The collector itself needs a lot of work as well. Here are the issues we found with the collector.
  1. Our research has informed us that chlorine is corrosive in its interaction with copper and thus for systems that utilize copper a heat exchanger (closed-loop) system or a chlorine alternative are strongly recommended.
  2. The solar collector is much to small for the desired function. When we tested the system, the water moved through the copper pipes much too quickly to absorb any substantial amount of heat.
  3. The actual design of the collector may not be the most appropriate for the given situation. The copper was used by the previous team because it was available at the time, but in order for the system to be at a suitable size to heat the pool, it must be much bigger and copper is very expensive too source locally.
  4. The insulation of the system as a whole is very poor. The collector itself needs insulation underneath it to prevent the transfer of heat to the cement roof. The pipes that transfer the water to and from the roof also have a high potential to transfer heat into the walls and should be insulated to maximize efficiency.

Potential Solutions[edit | edit source]

  • We invited a local plumber/pump salesman to come out and examine the system. His recommendations where useful to help us design a plumbing configuration that utilizes filtered water. This would solve a number of problems associated with the current system configuration.
  1. The solar collector system would be in line with the filter pumps and could use the power of them to pump the water to the collector, thus eliminating the need for the small, underpowered pump.
  2. The issues with the unfiltered water clogging the system and returning to the pool would be eliminated.
  • As far as the collector itself is concerned, we tried to take a step back and look at this project as a whole. We tried to determine the most appropriate approach to heating the pool. After further examination of the available materials in Parras and the efficiency of the current system, Ignacio is now looking for a commercially manufactured collector to increase efficiency and hopefully keep costs to a minimum. This appears to be the most appropriate approach at this point and helping Ignacio determine what an appropriate system would look like became our priority.

Excel Programs[edit | edit source]

Below are links to semi-completed Excel worksheets from RETScreen. This extensive program helps size systems according to the collector type. Each link corresponds to the specific systems we entered into the program. We included Evacuated Tube Collectors, Polypropylene/Unglazed Collectors, Glazed/Flat Plate Collectors, as well as an analysis of the current system. The designers of the Excel program included a PDF document to facilitate the understanding and use of the program. We have included this document as well. The current system analysis may not be as accurate as the others as the program is designed for a more standardized/commercial collector. The figures on the costs pages were the hardest to determine and may vary from location to location. We had trouble finding costs of systems in Mexico, so 20% was added to the price of collectors found in the United States as a shipping/importation estimate.

Evacuated Tube Collector[edit | edit source]

Evacuated Tube.xls

Polypropylene/Unglazed Collector[edit | edit source]

Unglazed workseet.xls

Current Perote System[edit | edit source]

Perote System.xls

More Discussion[edit | edit source]

See the talk page for more information and conversation about this project.

Related projects[edit | edit source]

External links[edit | edit source]

"Water Heater Efficiency" [1]

"Energy From Natural Gas" [2]

Suggested links for the 2007 team[edit | edit source]

Start with these basics. Notice the other link to this same site listed below that adresses system sizing.
Solar hot water basics from Australia Gov, UK Gov (44 pages) and private industry.
Some info on solar swimming pools, but it suggests using the pool´s filter pumps which may not work in your case (but are we sure?).
Sizing a Solar Swimming Pool Heating System.
Good narrative on sizing pumps. Nothing about solar, but some good pointers. It is missing images.
Some pool pump sizing information.
Nice pump curves (page 36).
How to read a pump table (please note that this is from an irrigation pump, but the table style still applies).

Discussion[View | Edit]

What's up 2007 team?[edit source]

Hi, this is Aaron Antrim, one of the project team members from 2006. Feel free to bounce stuff my way during your work this summer. What's the present condition/status of the system? --Aaron 00:23, 15 July 2007 (PDT)

C'est la vie[edit source]

Hola Aaron,

Oh la la, the present condition/status of the system? Well considering we haven't touched it yet, probably about the same as when you left it. When we first sat down to talk with Nacho about it, he was telling us that it works great and they use it when they want the pool a little warmer in the summertime. Then when we were down there checking it out, the maintainance guy told us that they had turned it on once, but the pump "got tired" and hot, so they turned it off.

Currently we are waiting for Nacho to come back from Saltillo with some special PVC parts. According to Oswaldo, a plumber friend of the boys, we need to hook the system up so that the main pool pump pushes the water to the roof. While that is happening we will check the amps to see if the work load stresses out the pump too much. If not, cool, we don't have to think about buying a new pump. From that we can supposedly get some figures to plug into an equation to see how big the system would have to be to actually get the pool up to 80ºF. My question is this: what is that equation? How in the world do we actually figure out how big the system needs to be? How do we make the connection between the prototype and the real deal? Any ideas you can supply us with would be more than appreciated. All the research I've found thus far on the internet is extremely vague and ends by saying that working with a professional es el mejor. Thanks for nothing! is always the feeling I come away with. I'm sure your'e quite intimate with that feeling after working on this project last year?

Muchas gracias, Carolina --waterfaery72

How to calculate the necessary size of the system[edit source]

Well we started trying to answer that same question (what system size is necessary to heat the pool to the desired temperature) last year. Here was the way we thought to figure it, if I remember correctly:
(1) What is the rate of the pump and volume of water contained in the solar collector? How much water is cycled through per minute (volume of water processed) and how long does it stay in the collector (how many degrees hotter will the water be when it's returned to the pool).
(2) How much of that heat will be lost, and how quickly, from the pool. There will be some cooling that happens in the pipes that come down from the roof (could be reduced with insulation). But you may be able to find equations to help calculate how much heat will be lost based on the surface area of the pool, or another approach might be to measure how much temperature loss occurs in the pool overnight. I have no idea how the rate of temp loss will be affected by a great temp. difference between pool and air in winter. Oh, as a side note, a pool cover is super-important for having any hope of making this system viable in the winter.
In short, what we were trying to do was calculate (Temp gain from the system over the course of a day) minus (Temp loss from heat transfer in the pool over the course of the day/night). Good luck! --Aaron 13:17, 23 July 2007 (PDT)

One 2007 Team Member Reflects a.k.a Jonathan[edit source]

August 11th, 2007

As individuals within a team we all experience and value certain aspects of our experiences differently. For that, I would like to add some personal notes on the development of the Perote project.

  • Miscommunication, lack of communication, or misunderstanding has led to an inappropriate use of time, money, materials.
  • There is a lot to be learned from this.

Tybie writes in her winter notes that in asking why her teams design had not been implemented that the technicians told her that the design need to be changed and they were waiting for the next team to approve the new design. Tybie did not personally take credit for approving the new design and left out whether she had and how she consulted her team about the change. But she does mention that construction of the new design was completed during her winter visit. This is unfortunate for our team had to wrestle with the politics and economics of reconstructing the system. This was a great learning experience on our behalf but it was also very time consuming, and a tad exhausting for those involved.

  • Nobody likes to be told that a mistake was made and we'll have to go back and do it again - especially when their time, money and property is involved.
  • In my opinion this error, while not fatal by any means, has negatively effected Ignacio's opinion of the project and has swayed his confidence to move it forward.
  • Mistakes were made, waste is involved, and we have responsibility to acknowledge and correct that.

It is unfortunate that our team was not able to pull together the commitment and resources necessary to reconstruct this aspect of the system so that "Nacho" could feel good about where things are at, and next years team could jump right in to focusing on testing flow and temperature, collector expansion and/or moving in the direction of sourcing a more appropriate collector.

Another aspect of the unattended construction and faulty design in connecting the collector to the pump system is for some reason Ignacio's workers felt compelled to tell him that the system is was working fine, they run it and it makes a difference in the temperature of the pool, but not much. That would have been very nice were it true, but it is not and we had to tell Nacho so on as well as that in our opinion the work was a mistake.

  • After bringing Ignacio together with our plumber and his technicians he is now well aware of where the system is at and what needs to be done to get water running through the collector in our opinion.

I have talked with him about it a few times since and tried to cultivate confidence in that regardless of where he goes from here he was going to have to address the pump issue to get water up to whatever collector he would ultimately invest in.

  • We assured him that we would test closely the amperage and temperature of his filter pump in insure that it can handle the added work load - I am fairly confident it can since most all systems we've researched worked in this pattern.
  • Ignacio is very careful with his money and it may require team contribution at the very least to reassert confidence in him of our commitment to the project.

To work that is required to realign the pump system to work with the filtration system is minimal and should be inexpensive. Their is not doubt one could do it themselves but I strongly recommend that you work with Ignacio's technicians or volunteer to source a plumber from town to keep things suave.

  • Our plumber, Oswaldo Alvarado, is amiable, smart, familiar with the project and where it's at, and speaks a good english - which was integral to airing things out and bringing it together in my opinion.

Oswaldo, among other things, runs a little Bomba shop on Ramos Arizbe west of La Reforma and lives next door. He can be tracked down there - he's happy to help.

  • Polypropylene and Evacuated tube collectors are manufactured domestically by Heliocol Mexico.

More research needs to be done, but based on what we have, one will find that in warmer climates polypropylene dominate the solar pool heating market because they are cost-effective and work we in warm conditions. Mexico Solar is an installer based out of San Miguel de Allende that appears to do a lot of work with polypropylene collectors. Relevantly, San Miguel de Allende has a very similar climate to Parras de la Fuente in terms of average lows during the colder months: click on the pueblos to see average temperatures.

  • Evacuated tube collectors may be the most effective way to keep the pool a comfortable temperature in the colder months and in indirect light.

If ultimately it is the goal of Ignacio to extend his swimming season to year-round or near that, evacuated tube collectors (ETC) may be the most appropriate technology to meet that goal. While per meter squared it is true ETCs are relatively expensive to alternatives the amount required to heat a large body of water is significantly less. Based on the calculations of a UK ETC company it would take roughly 8 ETC's to get it done. That figure may actually be significantly lower considering average temperatures in the UK relative to here.

Be aware that I've heard through the grape vine that their is a significant leak in the filtration system that Ignacio has been able to isolate between the pump station and the pool. This is another set back for us as well as it is said that the leak is bad and for that reason the system is being run very infrequently which would explain numerous dirty pool sightings during even events such as weddings. I have been told the problem with fixing the leak is that one would have to dig up the new terrace along the lines, completely, to isolate and repair the leak.

  • The leak would have to be addressed along with our pump/collector correction before any serious attempts at warming the pool vis-a-vis solar thermal collector can be had.
  • A pool cover is the cheapest, easiest to use and maintain, and most effective technology that could be utilized to prevent heat loss.
  • Solar thermal collectors can work in Parras!

This is a great project that warrants engagement. Ignacio has given us a great opportunity to work in a commercial setting to construct a solar hot water system in the middle of a 500 years old hacienda. Super padre!

See also: For more info on San Miguel de Allende

~Jonathan Linton
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