RE: {District Cooling Forum} Very low-temperature district cooling system des...
Rickey Naidoo
Dear John,
Thanks for your input. Much appreciated.
The design that I am working on is a chilled water storage plant not stratified tanks.
I have noticed from past experience that there is always been an element of mixing in stratified installations.
My new design has been concentrated on, no mixing of chilled water and no glycol as our design temperature is 38.3 F.
I have designed the rolling tank method which completely eliminates any form of mixing of chilled water. This coupled with low temperature water offers enormous benefits to the Thermal storage plant installation.
In actual fact, I was able to design this plant plant at almost the cost of a conventional plant. Thermal storage plants using ice plants, as you may well be aware is approximately 1.4 to 1.6% more expensive than conventional systems.
The design being such, has resulted in there not being a motivation for payback periods as the plant starts to save money immediately.
In South Africa, there is no installations using low temperature 38.3F supplied to AHU’s. The conventional 42.8 F has always been used.
We have used lower temperature water on the primary circuit but this has always been mixed/ combined with plate heat exchanger- with the return water to supply 42.8F to the building.
Please let me know if you have done similar installations.
Rickey Naidoo
Pr Tech (Eng) M Tech ( Eng) GCC fact. MASHRAE
Naidoo & Associates
Consulting Mechanical Engineers
30 Tamarind Cl
Somerset Park
Umhlanga
Tel/ Fax 0315621706
cell 0829591278
Non-performers focus on obstacles. Performers focus on results.
~Nido Qubein
From: Coolsol...@aol.com [mailto:Coolsol...@aol.com]
Sent: Monday, September 15, 2014 9:31 PM
To: jho...@stny.rr.com; district-co...@googlegroups.com
Cc: ric...@telkomsa.net
Subject: Re: {District Cooling Forum} Very low-temperature district cooling system des...
Dear Rickey,
Like you, I too am a consulting mechanical engineer; my business focuses on consulting related to TES, District Cooling, and Turbine Inlet Cooling. I concur with your Low Temp Water TES concept and the benefits you mention relative to non-TES systems and to Ice TES and Water-Glycol TES systems.
I am assuming that the concept uses water TES which is thermally stratified (less dense CHWR over more dense CHWS) in a single insulated TES tank, as has become quite standard for several decades now. The minimum CHWS temperature limit for thermal stratification of plain (pure) water is theoretically 39.4 degF (4.1 degC), which is the temperature at which maximum density occurs for pure water. It is common to have some impurities dissolved in the water (a few hundred ppm) as well as some water treatment chemicals for corrosion inhibition and microbio control (perhaps several hundred to one thousand ppm). Thus it is possible to stratify the water at temperatures very slightly below the 39.4 degF minimum for pure water. Your suggested supply temp of 38.3 degF may be slightly lower than you can actually achieve with nominally pure water.
There have been a number of stratified Low Temp Fluid (LTF) TES installations installed, operating at CHWS temps well below the pure water minimum. Some have a supply temp as warm as 36 degF, while others are as low as 30 degF or less. In each case, they use an aqueous fluid with dissolved corrosion-inhibiting salts, in a concentration (from 3 to 7 weight %) chosen to suit the desired supply temperature. This LTF TES system is patented and uses the trade name SoCool. This LTF compares very well with water-glycols, as the LTF is relatively low cost, has thermophysical properties quite close to those of plain water, and also eliminates the need for on-going water treatment for corrosion and microbio control.
Accordingly, your suggested Low Temp Water TES approach for DC makes good sense, but may be limited to minimum supply temps of ~39 degF. For much colder supply temps, SoCool TES can be, and has been, used.
Please contact me anytime, if you have further TES-related questions.
John
John S. Andrepont, President
The Cool Solutions Company
5007 Lincoln Avenue, Suite 201
Lisle, Illinois 60532 U.S.A.
tel: +1-630-353-9690
fax: +1-630-353-9691
e-mail: CoolSol...@aol.com
website: www.CoolSolutionsCo.com
In a message dated 9/15/2014 1:14:24 P.M. Central Daylight Time, jho...@stny.rr.com writes:
Len,
The best person for this request would be John Andrepont.
Joseph C. Hoose
On Sep 15, 2014, at 2:07 PM, Len-IDEA <len....@gmail.com> wrote:Posted on behalf of Rickey Naidoo, a consulting mechanical engineer in South Africa seeking comments from IDEA on his very low temperature non-glycol, non-ice district cooling design using water for TES; your reply will automatically be emailed to him.
I am South African consulting engineer located in South Africa and have designed a thermal storage plant using supply chilled water temperature of 38.3 F returning at 53.6 F (12F). I am interested to know if there are any similar applications using 38.3F chilled water in the US and would be interested to know of the challenges that has been experienced using colder water.
I have opted to make chilled water as I wanted to stay away from Glycol and ice plants.Trane makes a chiller can safely make chilled water at 38.3 F.
The net effect of this design promises the following benefits:
- The chillers ( the source of making the chilled water) reduced in capacity by almost 50%
- Due to the type of chiller used, the water could be stored down to 3.5⁰C without the use of Glycol. ( Glycol is used to lower the freezing point of water to protect the chillers and is very costly in storage applications). Chilled water is normally used at 6⁰C in chilled water applications.
- The chilled water storage capacity was reduced by almost 40%
- There was a huge reduction in the cost of the air conditioning installation as there was no major storage capital equipment used. The only major cost was the cost of the thermal storage tanks.
- The chilled water pipe sizes to the building was reduced due to the reduced water supply temperature. (In at 3.5⁰C; out 12⁰C). This offered substantial savings to the project. Reduced air-handling unit sizes due to the larger temperature difference across the cooling coils
- Reduced pump sizes due to the 30% lesser water being pumped to the building.
- No payback motivation required as the cost of the thermal storage plant was equal or cheaper than a conventional chilled water air conditioning system. Conventional air conditioning systems does not use storage. The chilled is sized on the full size chillers required to satisfy the air conditioning to the building.
- Huge electrical savings as the plant does not work on maximum demand periods using the local 2 part electrical tariff. The client only pays for reduced cost energy charges, which are billed at a cheaper rate at night.
- 42% cheaper energy consumption when compared to a glycol chiller making ice on a Calmac installation. Glycol chiller COP is 3.9 whilst the chiller making chilled water at 3.5⁰C operates at a COP of 5.6 during the night charge of the chiller.
- Lower maintenance system as no Glycol is used on the system. Glycol installations are very corrosive to the valves and fittings.
- Unlimited lifespan as the chilled water tanks can last for a very long time.
- Simple controls for the mechanical installation.
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Coolsol...@aol.com
Hi Rickey,
Yes, 36 F all the way to the coils and the design was original to the airport construction (very innovative for 1970).
We did some coil control valve changes as part of a major renovation and a new terminal construction to achieve a >24 F design delta T using 1/3 and 2/3 coil flow split control. In some cases we achieved 28 degrees, which blended with older terminal returns (which were less than 24) to average the 24 F delta we needed for the tank design.
Yes, it was a stratified water tank.
SoCool depresses the maximum density/temperature relationship (below 39.1 F), such that mixing does not occur.
We had a very tight stratification layer, approximately 1-2 feet (<3%) on a 60 foot tall tank.
Feel free to call me at (817) 840-1233, if you have further questions.
Best Regards,
Scott
From: Rickey Naidoo [mailto:ric...@telkomsa.net]
Sent: Tuesday, September 16, 2014 9:17 AM
To: Clark, Scott; district-co...@googlegroups.com
Subject: RE: {District Cooling Forum} Very low-temperature district cooling system design from South Africa using water for TES.
Great stuff,
I would be interested to know if 36 F water was supplied to the AHU’s and what precautions you have taken for the insulation.
Also, was this a stratified tank installation ?
The design that I am currently working on is chilled water thermal storage plant. I have had extensive experience with stratified tanks and have still found mixing on the installations.
I have designed the rolling tanks method, which completely eliminates mixing and combined this with low temperature water to achieve enormous savings on the thermal storage plant applications.
Many thanks for your input.
Rickey
From: Clark, Scott [mailto:spc...@burnsmcd.com]
Sent: Monday, September 15, 2014 9:53 PM
To: district-co...@googlegroups.com
Cc: ric...@telkomsa.net
Subject: RE: {District Cooling Forum} Very low-temperature district cooling system design from South Africa using water for TES.
We did a similar design at DFW Airport using 36 F degree supply, with SoCool, and a 60 degree F return. The tank is 6 MG and 90,000 ton-hours.
It’s been in operation since 2004 with good success.
There was a minimal de-rate to the chillers, but it was not significant.
Thanks,
Scott Clark, P.E., CEM
Practice Leader, OnSite Energy & Power
Burns & McDonnell
6500 West Freeway, Suite 700
Fort Worth, Texas 76116
817.840.1233 Office
817.233.1540 Mobile
Proud to be #14 on FORTUNE's 2014 List of 100 Best Companies to Work For
* Registered Engineer in Texas
This e-mail and any attachments are solely for the use of the addressed recipients and may contain privileged client communication or privileged work product. If you are not the intended recipient, and receive this communication, please contact the sender by phone at 817.840.1233 and delete and purge this e-mail from your e-mail system and destroy any other electronic or printed copies. Thank you for your cooperation.
From: district-co...@googlegroups.com [mailto:district-co...@googlegroups.com] On Behalf Of Edward T. Borer Jr.
Sent: Monday, September 15, 2014 1:16 PM
To: district-co...@googlegroups.com
Cc: ric...@telkomsa.net
Subject: RE: {District Cooling Forum} Very low-temperature district cooling system design from South Africa using water for TES.
Princeton (and many other plants) use water as cold as 31-degrees F. We use a 5.7% solution of nitrite/nitrate with a trade name of SoCool. That product allows us to store very cold water in a thermally stratified chilled water application. It won’t freeze until somewhere in the range of 25F. It results in a slightly different density and specific heat than water, so pumps and heat exchangers should be designed with this in mind. We do not operate colder than 31F so that un-treated water on the other side of a heat exchanger will not freeze.
Our thermal storage system is 2.6 million gallons. With a 20 degree differential temperature, that results in about 40,000 ton-hours of storage.
Glycol tends to be food for biological contamination. At the concentration we use, the nitrite/nitrate solution is an effective corrosion inhibitor and biological inhibitor. We have never had a problem with biological growth or corrosion since the system was installed in 2005.
Ted Borer, PE, CEM, LEED AP
Princeton University
Energy Plant Manager
MacMillan Building, Elm Drive
Princeton, NJ 08543-2158
Ph:(609) 258-3966
Fx:(609) 258-1508
Cell: (609) 731-2327
Home: (609) 466-3322
Learn about our plant on YouTube: http://www.youtube.com/watch?v=xwHhbDvpdS4
Rickey Naidoo
I think the concept is similar but we only use 3 tanks -50% redundancy. I don’t know of any installations done previously.
Total volume of storage water is stored into 2 tanks with 1 tank empty.
Return water or generated chilled water fills the empty tank without any mixing.
Our chilled water storage is based on a rolling tank method.
The design consists of 3 tanks. Each tank capable of holding 50% water.
At night tanks 2 and 3 are filled of water. ( common and hot tanks)
The charging Night cycle works as follows :-
Water is drawn from common tank 2 and passes the the chiller to make 3.5 ⁰C water. Chilled water is accumulated into cold tank 1 until tank 2 becomes empty.
Common tank 2 valve closes. Water is now drawn from Hot tank 3.
Water is then drawn from hot tank 3 and filled into cold tank 1. Tank 1 will overflow into tank 2. Plant will run until hot tank 3 is empty and common tank 2 is full.
Day cycle works as follows :-
You will have cold tank 1 and common tank full of cold water.
Cold Water is drawn from common tank 2 and passes the the airhandling units to cool the building. Hot water will empty into Hot tank 3 which is empty.
As common tank 2 becomes depleted, hot tank 3 becomes full.
Once common tank 2 becomes empty, tank valve 2 closes and tank valve 1 opens. Hot water from tank 3 will overflow into common tank 2.
Rickey