steve@engineeringtricks.com

Pool Care – Part 1

Introduction

I live in upstate New York and have a rectangular in-ground vinyl lined pool. I use chlorine tablets and have a Diatomaceous Earth filter. I also have a natural gas fired heater in the pool. I can usually swim from mid-May through the end of September. My pool is older so it still has a bottom drain. The newer pools have a return line in the bottom drain.

Opening

I usually start opening the pool in early May. My criteria for opening is the second day of the spring to rise above 80F. I have a loop lock cover and fold the cover from one end to the other. This prevents any debris on top of the cover from falling into the pool. The filter plugs and other small parts are kept in the strainer basket.

(All pools are different, discuss these instructions with your pool service professional for your pool.)

Removing the cover

This can be removed with just one person. The important Start at one end of the pool and remove the springs from the end and one on each side. Fold the cover over so that the seam is at the second side anchors. Remove the spring from one side and fold one half way over. Unhook the spring on the opposite side and fold the rest of the way over. Continue down each side in the same manner. When you get to the last side anchor make sure the cover is completely out of the pool before disconnecting. The anchors are usually tightened with an Allen Wrench. Caution before you tighten them, remove and vacuum out the hole and anchor otherwise grit can cause the anchors to jam. Tighten the anchors so that are flush with the concrete.

Starting the Pool Pump

Note: (Each system may be slightly different and it is best to check with your pool service)
1. If there is large debris (leaves branches, dead animals), remove those prior to starting of pump.
2. Install pool ladders and stairs
3. Reinstall the plugs for the pump and filter. Reinstall the pressure gage on top of the filter.
4. Fill pool so that water level is a half way up the skimmer.
5. Remove plugs from the following locations
• Return lines in pool
• Skimmer
• Inlet to strainer basket at suction of pump
• Open skimmer line valve
• If you have a bottom drain make sure that is closed as well.
6. Open the cover to the strainer basket on the filter. Remove any debris in the strainer. If the strainer basket was removed, reinstall Overfill pool suction strainer with water. This will fill the line to the skimmer.
7. Close the cover to pump suction basket.
8. Open filter bypass (this is also the recirculation valve position on a 5-way valve)
9. Install skimmer basket
10. Turn on pool pump, wait about a minute for water to come out of the return lines to the pool.
a. If the water does not start or the pool pump is making unusual noise, turn off the pump and check with pool service professional
11. Turn off pump
12. Close filter bypass and open filter valve (this is also the filter valve position on a 5-way valve)
13. Turn on pump
14. Install water jet fittings on return lines.
15. Add filter aid in skimmer according to manufacturer’s instructions.
16. Let pool run for 4-8 hours.
17. Grab a small sample of water and bring it to pool service to get water tested.
18. Add chemicals and additives as directed by pool supply.
19. Once chemicals are added and pool has been running, you can turn the heater on the pool.
20. If you are opening it in the spring, the use of a solar cover is recommended especially at night.

Heating & Solar Covers

I have a gas water heater and can usually raise the water temperature at 1 F per hour, so raising it from 55 degrees F to 80F takes about 25 hours. I have a rated 200,000 BTU/hr. heater so @ 20,000 gallons this would require 4,170,000 BTU (20,000 lb./ gal X 8.34 lb./gal * 25 F * 1BTU/hr./F). At 200,000 BTU/hr.) and take 21 hours if there was no loss of heat.
Incidentally, I have a 180,000 BTU/hr. hot water boiler to heat my house, so my pool heater is larger.

I have found there are critical times to use a solar cover. If the humidity is low and the clouds are clear at night. If you don’t use a solar cover on these nights, then there will be evaporative cooling and the water level will drop and the pool will become significantly colder. How much colder depends on the temperature, wind speed, humidity and aeration of the water surface.

In Part 2 – I will discuss chemistry of pool care and pool cleaning

Fastest Way to Cool Your Favorite Beverage

Imagine it being a hot afternoon and you just finished working outside in the hot sun. You decide to cool off with a cold beverage. Much to your dismay, someone forgot to put the beverages in the refrigerator. Now you are stuck. You do not want to drink a beverage such as water, ice tea or a carbonated beverage that is at room temperature. You want to drink it, but it is too warm. You would prefer a temperature of 42F. What is the fastest way to cool down this beverage so you can drink it as soon as possible?

There are many options to cool down your beverage. Some of these are the following:

Stick it in the refrigerator – this is great if you have the time.
Stick it in the freezer – Watch out for freezing
Run cold water over it –Hope you have plenty of cold water
Stick it in an ice bath –
Stick it in a crushed ice bath (In the winter you could also stick it into a snow bank).
Stick it in a water and ice bath
Rotate it in a water and ice bath
Put ice cubes directly in it.

Experiment Design

In order to test the above options over a wide range of containers and bottles, the following items were used in the experiment:

A digital thermometer
A one half liter plastic water bottle (16.9 oz.)
1 glass ice tea bottle (16 oz.)
A 12-ounce non-carbonated beverage can. Note – a carbonated beverage would have worked have been used, except I put a small hole in the top of the can for the thermometer and the carbonated beverage would have fizzled out of the can.

The goal of each test is to reduce the temperature from 70 F to 42F.

The following is a tabulation of results

The first value is for the 16.9 ounce plastic bottled followed by the 16 ounce glass beverage and 12 ounce aluminum can. All times are in minutes.

Refrigerator – 463, 457, 305
Freezer – 62, 51, 22
Cold Water running over can – Neither container met goal of 42F
Ice Bath – packed around beverage – 51, 55, 12
Crushed Ice – packed around beverage – 20, 18, 8
Ice and Water Bath – – 13, 15, 6
Rotated can or bottle in Ice and water bath in insulated bin – 6.5, 6, 3.5
Rotated can or bottle in salt & Ice and water bath in insulated bin – 6.5, 6, 3.5

Comments

Refrigerator – Great for overnight or all day cooling
Freezer – Possible danger of breakage if left unattended
Cold Water running over can – Big waste of water, tap water is at 59F
Ice Bath – packed around beverage – Time included partial melting of ice cubes as it cooled down the beverage
Crushed Ice – packed around beverage – Times do not include crushing ice
Ice and Water Bath – Great for multiple bottles
Rotated can or bottle in Ice and water bath in insulated bin – Fastest undiluted method
Rotated can or bottle in salt & Ice and water bath in insulated bin – Although the salt lowers the bath temperature to 28F, it didn’t have an appreciable effect on the time to cool it to 42F. This is useful if you wanted to reduce the temperature of the beverage below 40F

Conclusions

The refrigerator was the slowest because it had the lowest differential of final temperature. The freezer works faster if one remembers to remove it prior to freezing. Crushing the ice increase the surface contact with the beverage and thus has more conductive heat transfer. Adding water to the ice removes the air space which is a very poor thermal conductor. Rotating the beverage container allowed mixing of the fluid inside the can, which accelerated the heat transfer. Adding salt to the fastest time didn’t reduce the time, but did allow for a colder beverage below 42F.

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