HVAC Question - Water Cooled Chiller

A LOT smaller size for for the same capacity.

Water has a higher heat transfer coefficient and higher heat capacity than air.

Guest #1 cont'd

For example:

'h' the heat transfer coefficients can be 2 orders of magnitude different.

• Air - 10 to 100 W/m²K
• Water - 500 to 10 000 W/m²K

Water has an even bigger advantage over air for use in cooling or heating thats never used as far as I can see. Water can be cooled by maintaining a low pressure boiler so the water boils at ~10C. The vapor can be compressed and condensed in the atmosphere thereby transporting heat out or evaporation can be done at the other end to move heat inside. Use of water is a much less costly way to transport heat in and out to heat or cool.

In a water/lithium bromide absorption chiller, water is used as the refrigerant and LiBr as the absorbent. The evaporating temperature of the water is approximately the 10°C you described. In a hot, dry climate it should be feasible to power the regenerator by focused solar heat. A black pipe solar collector might even be enough, or nearly so.

I suspect this scheme would be a prime subject for Salahuddin's investigation.

I Worked in HVAC for 16 yrs. If you are familiar with how cooling towers work, they do use the cooling quality of water to enhance standard refrigerant systems. these systems are only seen on large commercial buildings but could be rigged up for your home. The huge systems run the hot compressed refrigerant through a small compact system within the building, the evaporator coil is inside the ductwork and works the same as any household system. The Condenser is inside a water jacket (water runs over the coils instead of air like a residential system) the hot water is pumped to the roof where it falls like rain into a huge cooling tower/house. the cooling tower has blowers that help cool the hot water and after it is chilled it is sent back down to cool the hot condenser coils. I have often thought this type of system could greatly reduce residential systems energy costs, but have never designed a system to do it. If anyone is interested in working on it I would love to collaborate on it. Thanx Harold

Hi Haroldoftroy, It has been a few years since any activity has occured on this topic. I am very interested in developing a well engineered heat moving device. The current state of art(as you well know)fails to move heat efficiently no matter what off the shelf machinery is chosen.

Energy requirements are less if a cooling tower is used instead of ambient air. A cooling tower produces water at around 85 degrees F, versus ambient air at 100 degrees F (+/-). Water has a much higher specific heat compared to air. The compressor simply sees a much lower condensing temperature and presssue on its discharge side (around 85 degrees F) compared to ambient air at 105 degrees F (I'm from Texas).

The first thing to consider is, "do you have a cooling tower" If so I agree with everyone that water cooled is better. If you have to invest in a cooling tower, that will cost you more. The other question is, "what size chiller are we talking about 6 ton or 106 ton?" Makes a big difference when discussing water or air cooled.

A cooling tower still trafers heat to the atmosphere even if it does so at lower temps than an air cooled condenser. Its a trade off between energy and water so it all depends where the system is located. The low pressure boiler can be used in both air and water cooled condensers. Its just more efficient to move heat from ~10Cto50C using water but maybe better solar powered cooling can be developed that I don't know anything about. Are there links to useful(rather than useless) info about this? As for water cooled chillers, it seems a lot of engineering needs to be done to develop a really good system. Lots of details need to be worked on.

The OP is rather unspecific.

A water-cooled shell/tube or plate/frame condenser can offer the advantages of compact size and lower refrigerant condensing temperature/pressure. This may save considerably on compressor power, and the water pump will likely also need a bit less power than the fans for an air-cooled condenser. Some disadvantages are that it needs a large supply of water; it warms up the water, which may not be environmentally acceptable; it may experience erosion from particulates in the water, etc.

An air-cooled condenser will be much larger, and especially in hot climates it will result in greater compressor power and higher condensing temperature. Except for perhaps some water cooling for the compressor, there may not be a need at all for water.

An evaporative condenser is somewhat in between the other two, in most respects.

***

On the evaporator side, a lithium bromide chiller is a perfect example of a low-pressure boiler. Whoever voted the earlier post as OT is remarkably ill-informed about refrigeration, and also lacks vision.

Although you will certainly have better net efficiency, there are several disadvantages to consider for the water cooled chiller with cooling tower. First, it is more complicated. You have an extra pump to serve the condenser water to the cooling tower. This energy needs to be applied to your net efficiency. Next, cooling towers require a lot of maintenance and consideration. There is scaling, corrosion, rust, algae, sun damage, ugliness, high sound levels, freeze protection, health issues, and general maintenance. Cooling towers can use a lot more water than you think, based on the local wet bulb temperature. This cost should technically be be factored into the net efficiency. The owner of a cooling tower really needs a good maintenance person to look after it.

Good point on the additional cost on chemical treatment, the more water the more chemical, if you don't have a competent chemical treatment program you can virtually destroy the system and related equipment with in one year depending on the quality of available water. I have seen this happen in a process application.