DIY Bed Cooler

19 November 2012

Introduction

To many in the topical countries, air conditioner is an essential thing to have for a good night sleep. A room air conditioner, operating 10 hours per day, will consume roughly about SGD$60 of electricity per month; out of which, 90% is wasted in cooling the room and the walls. This article will share how this much energy can be saved by using a bed cooler.
Note: The same set up can be used for bed heater by using aquarium heaters

What’s a Bed Cooler?

A bed cooler cools only the bed instead of the whole room. It runs chilled water underneath the bed sheet or mattress. To cool an average size room, one will need a cooling capacity of about 10,000 BTU/hr or 2,800 cooling watts; but to cool a person, one will need only 1/20 of this energy; hence, about 90% of the energy could be saved.

What’s Available in the Market?

There are a few brands of bed cooler available in the market. Most sold with a cooling mattress plus a heat pump unit that can generate either hot or cold water. It costs around SGD$800 for a single bed and about SGD$1,300 for a king sized double bed.

What Are the Components?

Each bed cooler consists of a mattress either embedded with silicone tubes or PVC sheets sealed to form tubes for chilled water to be run within.

The cooling or heating water is often generated by an electronic Peltier chip that is powered by a 12 or 24 volts power supply. It has also a pump and a temperature controller where temperature can be controlled or set remotely.   One forumer claimed that he saved about 50% in the September 2012 electricity bill after using the bed cooler.

A Chinese video explaining the workings of a bed cooler can be found here

Where To Buy the Components for DIYs?

For DIY enthusiasts, the bed cooler components including Peltier chips can be purchased all from Ebay. A refrigeration kit consisted of 2 pieces of 60 watts cooling power Peltier chips plus heat sinks, fans etc will cost not more than SGD$50.

Its cooling power is just barely enough for a single bed application after some de-rating.  The other costly items are pump, silicone tubing and a temperature controller (also available from ebay) which may cost another SGD$60 for a single bed. The silicone tubes and pumps can be purchased from local aquarium shops. One enthusiast has constructed an aquarium chiller using Peltier chip and his set up can also be used for the bed cooler project.
One could also buy the water cooling mattress and the temperature controller from China. The set will be cheaper but some said they were not as reliable as buying the complete mattress set from the local stores.

Other Alternatives?

Bar or mini refrigerators will not have the required cooling power for the cooler bed project. A bar refrigerator only have a cooling power of around 70 watts or 250 BTU/hr which is too small for a human load that is around 100 watts or 350 BTU/hr.

One could use an aquarium chiller instead of Peltier chiller except that one may need another circulating pump and a pump sump because the chiller often needs higher flow rate for proper operation.

What is the Set up for the DIY Project?

This article uses an old Resun Aquarium chiller model CL650 for the DIY project that was designed to cool a king size bed of 1.9m x 1.8m. The author got this chiller including the water pump for just SGD$50/= because one reef keeper gave up his hobby while moving his house. The final set up is as shown.

The Pros and Cons of this DIY Vs Commercial Bed Cooler

Pros

1. Aquarium chillers of Freon type are 75% more energy efficient than Peltier chillers. It has a Coefficient of Performance(COP) of 1.3 vs Peltier chiller which has only around 0.55;

2. For DIY, one can suitably place the chiller remote for minimum noise and better ventilation;

3. Can DIY to suit individual requirement

Cons

1. Cannot provide hot water for heating unless a heater is incorporated;

2. Only manual setting although starting and stopping can be controlled remotely by using a remote controlled socket;

3. Not portable and occupy more space.

What Size of Chiller?

The CL650 has a cooling power of 650 watts (1/4 hp) which is over sized for the project. The bigger size chiller will consume slightly more energy but will bring water temperature quicker to the set point temperature. A 300 watts cooling capacity or 1/8 hp chiller should be ideal for the project.

List of Components for DIY Project

The list of components and where to purchase them are as shown.

1) One aquarium chiller preferably 1/10 hp to 1/8 hp modified with external temperature probe;

2) One small aquarium tank insulated with 1/4” thick polyester form to house 2 pumps, a circulating and a chiller pump;

3) One 600 litres per hour(LPH) circulating pump and one 1800 LPH chiller pump as specified by chiller manufacturer;

4) One lots of 10 mm diameter PVC flexible tube from hardware store;

5) One lots of 6 mm diameter silicone tube for the bed cooling from aquarium shops;

6) 2 length of 20 mm diameter PVC plastic pipe as the header plus 2 rubber end caps and 2 pipe connectors for connection to 10 mm PVC tube from hardware stores;

7) 2 small tubes of super glue;

8) One 300 mm long balloon holding stick as stud for the joints between silicone tube and PVC pipes; outer diameter slightly larger the inner diameter of the silicon tube;

9) One lot of 1/4 “ thick sponge sheet from stationary shops, cut to form strips to wrap round the pipes and tubes;

10) One lot of shrinkable plastic tubing from hardware shops;

11) One mattress cover; hereafter referred to the mattress.

What is the most Difficult Part of the DIY Job?

The construction of the bed cooler mattress and the header pipe.

Header Pipe Construction

The header consists of 2 PVC pipe of 20 mm diameter and one 10 mm flexible PVC tube as a return to form a reversed return piping arrangement as shown. This will ensure that water is always first in and last out so that the pressures and water flow are equal in all the tubes.

The author tried 3 different versions to make a joint between the silicone tubes and the PVC pipe; two of which failed with multiple water leaks detected during the tests. The final and working version used a stud embedded in the silicone tube as shown.

First find a plastic tubing slightly larger than the diameter of the silicone tube. A balloon holding stick was chosen and cut into smaller pieces as shown in one of the smaller picture.

Do some experiment first with a short length of silicone tube and a short piece of PVC pipe. Select and drill a hole in the PVC pipe such that the hole should be just large enough to fit the stud loosely. When inserting the stub into the silicone tube, allow the tube to overlap for about 3 mm as shown. This will ensure that the tube can be first inserted into the PVC hole before pressing the stud into position to give the side pressure to seal the joint.

Drilling holes in PVC pipe accurately can be tricky and difficult unless one has a drill bench to hold the pipe in place.  The easier way is to DIY a simple tool using another short length of slightly larger pipe that can be slotted into the PVC pipe.  Drill at least 2 holes accurately on the larger pipe.  One of the holes will be used for alignment and the other for drilling a hole in the PVC pipe.

Elephant brand of super glue was used for the joint between silicone tube and the PVC pipe. With proper selection of the stub and the drill diameter, the stud should provide the required side pressure to make good tight seal for the joint.

This new version had only 2 joint failures out of the 48 joints which is less than 5%. A quick repair fixed the leak.

To facilitate the jointing process, each silicone tube is first rolled and tied up for ease of handling and also for ensuring the tube will be properly segregated for the joints to be made without making any cross over between the tubes.

Testing for leaks

After having completed the joints for the silicon tubes, it is important to test the joints for leakage if any. Pressure test the joints to at least twice the height difference between the pump and the bed plus any increase in pressure due to the pumping. If one does not have a pressure testing set, one could raise the testing pump to the required height as shown. Put old newspaper underneath the pipe for detection of any leak and do the repairs as necessary.

The Bed Cooler Mattress

Finally, lay the mattress flat on a cleaned floor surface and put the silicone tube etc in place with the PVC pipe header laid about 50 mm to 80 mm from the top edge of the mattress so that one can hide the header in-between the bed and the headboard. When the silicone tubes are laid in proper place, hold the tube in place by thread and needle, ensuring that no needle will ever punch a hole in the silicone tubes.

The details of the bed cooler mattress construction and the set up are as shown here.

Insulation and Vapour Sealing

The header and the 10 mm flexible PVC tubing that connects the header and the pump sump are then wrapped around with ¼” sponge strips, edge to edge to prevent condensation.

In addition, the header has a piece of cloth wrapping around and stitched to the end of the mattress to prevent any stress that may be put onto the joints due to pulling or shifting of the mattress during operation.

The connecting 10mm PVC tubing together with sponge strips is then sealed inside shrinkable plastic tubing often used for covering bamboo sticks.

Hiding the PVC header in between the headboard and the bed not only for aesthetic reason but also for extension of cooling to underneath the pillow where, at times, hands and arms putting underneath the pillow can be cooled for a good night sleep. Also, the joints are the weakest part. If there is a water leak, it won’t wet the bed.

To prevent the mattress from “running away”, there is a need to strap the mattress to the edges of the bed.

The Pump Sump

The author uses a 25 litres aquarium tank as a pump sump. It is then insulated with 2 layers of 1/4" thick  polyester foam to prevent condensation. Silicone glue was used on the edge of the foam to stick to the tank.  There will be a need to treat the water as bacteria will flourish also when there is air in the water.  Chlorinating the water is one best solution if one is using aquarium chiller and plastic pumps with porcelain shaft like Eheim.

Cost

The author uses most components from his store including an old 25 litres aquarium tank and the 600 LPH pump. The estimated additional cost was not more than SGD200/=. If new chiller and pumps are required, another SGD300/= may have to be added.

Testing and Performance

The consumption was measured by a data acquisition machine which recorded the energy consumption in minutes for 3 types of cooling for 3 different nights:

a) A Panasonic inverter air conditioning cooling the room @ 25^oC;

b) The bed cooler of this project, cutting in @ 23^oC and cutting out @ 25^oC;

c) The bed cooler plus Panasonic inverter air conditioning operating as an air dehumidifier with temperature set to 27^oC.


The result is as shown.

For the same bed and about the same weather condition, the cooler bed project saved about 90% of the energy bill. A variation is to use the cooler bed with existing air conditioner as a humidifier by turning up the air conditioner cooling from 25^oC to 27^oC. This variation will allow those who still want dehumidified air for good night sleep. The energy saving measured was around 50%.

Post Mortem

1. Equal Length of Silicone Tube

The author only estimated the length when cutting the silicone tube into pieces. This resulted tubes having different length causing unequal pressure and flow. During start up, more than 2 sets of tube have no water flow and hence,  no cooling on parts of the bed.  Fortunately, by lifting the PVC pipe header up and down several times solved the problem.

2. Stitching the tubes

When tubes were laid onto mattress, author started stitching from the header end, assuming the tube would have no crossovers. When he found the crossovers at the end, the tubes were all stitched in place. Therefore, it is important to start stitching from the ends first.

Other Observations

The Feeling of Silicone Tubes

One can feel the silicone tubes on the bed by finger touching but not the body. This is because only fingers and toes have sensory nerves.

Bed Heater

The bed cooler can be used also for bed heating purpose.   Some Aquarium chiller for example the Resun 650 has outlets for connection to external heaters such as aquarium heaters that can be immersed in the water tank. Resun's controller will regulate the temperature. Alternatively,  one could use the heater's thermostat to achieve similar result but the temperature control may not be so accurate.

Conclusion

The project has been successfully completed. It is a good project not only to save money but also to share the knowledge to others who can also benefit from it.

Update 1:  Leak Repair  1 April 2014

1.  The bed cooler finally leaked at the silicone joints to the PVC header.   Fortunately,  most leaks were  just minor triggering leaks that wet the bed liner and the header hiding the header pipes.  Repairs was done immediately within 30 minutes by disconnecting the outgoing pipe at the pump to prevent water back flow,  then cut the silicone tube and inserted a new stud.  The new joints had extended length of silicon rubber over the stud and a longer stud were used as shown.

To prevent leak from other joints,  all the joints were built up and covered by epoxy glue,   applied several coats, using a small brush over and around the exterior part of the joints.

2.  Sewing the silicone tubes to a bed cover was a bad idea as the bed cover could not be washed regularly.   The tubes were  now re-attached to 3 pieces of cloth;  2 of which were 10" wide with the header piece about 20",  allowing 10" to wrap the header pipes.   The clothes were then tied round to the bed using strings to fix the position.

3.  To support the header pipe, 2 pieces of  20 mm PVC pipe were cut and shaped to form pipe support stands as follows and placed at both ends of the header pipe to support the header pipe.  The flat part of the pipe support stand went under the bed cushion.

Update 2:   Air Lock in system

When there is air trapped inside the tube or pipe,  the pump will not work and no water will circulate.  To purge the air out,  reverse the input and output of the hose from the bed cooler.  If the pump is correctly sized,  one should see air bubbles purging out.  Repeat the process if necessary

References
How to Service Resun CL650 Aquarium Chillers
Freon vs Peltier Chiller for Reef Keeping
Cut Cooling Bills by 90%
Spot Cooling Cuts Aircond Bills by 50%
Bed Cooler A worthwhile investment