MPdesign

Referencing old and new water drinking fountains I have heard a recommendation to change the refrigerant every 2 years. Is there any truth to this and/or what is the reason? Thank you all for your help[:-thumbu] I have read on cars that some people recommend replacing the dryer after 2 years because of humidity gain through hoses and such and the dryer is full. This appears to require evacuation? Could this be it? What do you think?

OK. From the typical build of these, I assumed that the entire tube sheet could be removed from the shell and replaced. I would swear that a maintenance guy (on a very large one) said that they pulled out the tubes.

Can this be completed without removal of the insulation on the shell? i.e. from the inside after the tubes are removed.

Concerning a steam to heating hot water shell and tube heat exchanger (18"x12'), can these be tested? If so how and what are the budgets for doing so? Many of these are very old but they also usually last a long time.

Can you check the superheat and sub-cooling with the blower door off for max return air OR should I wait until another duct is added?

Update I turned the system off completely for 30 minutes. I then removed the blower door to get plenty of return airflow. No freeze was seen on any lines. It has been on for over an hour continuously. Air out of vents: 63 degrees. Return air temp 74 degrees. It is after dark now and cooler (84 degrees outside).

Thank you for the return air calculation. Thanks everyone!

Not a friend - he is the original condenser and coil installer (did not install ducts or furnace) I will measure the return but it should be about 78 - the temp of the house plus a few degrees. The guy mentioned something about super heat but he thought that the lack of return air could be throwing off all of the gauge readings somehow. Thanks for the blower door recommendation.

Thanks Terry! I have not seen any freezing on the lines coming out of the coil ever. I am not sure what superheat is? He only connected gauges at the condensing unit access points. So if I am understanding correctly, it may be cooling but the duct in the crawlspace is heating it up to 63 (in 15' distance) before it exits. My plan for testing is to cut the hole for another 8" return in the plenum and cover it with a filter. That should give me enough return air. Then if I run it and it is cooler, then I know that is the problem. I would only test this when the temp is cooler because I know it can only cool down 100 degree outside air so much. Will this work for testing? Any other recommendations. After testing, I will add another 8" return to that location. So it sounds like this may be my problem - but not all of my problem.

Hey guys. Hate to bother you with my own personal problems but those are the ones that hit my pocketbook the most. I bought the house last October. The coil and condensing unit were added at that time to a furnace and new ductwork both circa 2007. The house doesn't cool on hot days (3 ton - Atlanta - 1,500 SF, new windows, attic insulated) The guy just left and he had put gauges on the condensing unit initially and said that it was leaking. Said that because the pressure was just above 220 (I think) and should be over 300. I then showed him my return duct layout. My returns - I have 1@6" and 1@8". I knew this was not enough so I showed him. He changed his story and said that was definitely the problem and not a leak. He did appear to be a knowledgeable guy - more so than average - but he could not fully explain to me - so he does not fully understand himself. I would think that if not enough air crossed the coils that it would initially get VERY cool - until it froze up. The air coming out is only 63 at the closest register though... Is the lack of properly sized return duct really the culprit or is it the compressor/coil system? Note* the coil is enclosed with no access panel (above the furnace in the crawlspace) and cannot be viewed. Thank you for your valuable insight. [:-magnify Cheers

I have been out of electrical for while - so I may not bee 100% right on this; but I seem to remember the exception has to do with computed load. The load is computed and the next larger "standard" breaker size can be used. This is not your case.

Terry, Than you for the response. I am looking for budget numbers only. For AHU's (say 13' long x 10' high x 10' wide size) - assumes constant volume, heating water coils & chilled water coils. I normally see about 50/50 for pneumatic or ddc - so half the cost of the pneumatic adder. On filters, assume bag-less.

Just to add, these units are now the normal commercial retrofit application for a computer room. They are well thought out, proven overseas, and they make a lot of sense. Just ugly as h$ll.

Big push for these for "energy savings" as you only cool the rooms you use (at least that is the pitch). I think they are here to stay - but they are too ugly by most people's standards for normal everyday use. Commonplace overseas.

Gentleman, I am trying to nail down some costs for yearly maintenance on HVAC items. [:-magnify This should be based upon say a 10 million SF estimate across the USA. I have the following as a start - Please tell me what you think is high and low and why. Excluding water treatment costs. These include yearly maintenance and the cost of repairs (not replacement) that come up every few years Cooling tower - $300/yr Chiller (avg 400 tn) $5,500/yr AHU (standard office building size) $700/yr Pumps $200/yr (includes $100/year for repairs alone) boilers (1,000,000 btu/hr) $1,800/YR (includes $1,20/year for repairs alone) So, what do you think - and why? I have full faith and trust you as professionals.

Gentleman, Do any of you have a general cost expected for adding meters to the chiller to determine how long it runs in a year? Alternatively, can that data be extracted from the chiller typically (1990+)? The same for pumps? Looking to determine how how much they flow in a year. I need the cost for adding the metering equipment though. This is for process equipment not a building - so it cannot be modeled.

Link to 427A Dad was a building inspector, grew up on a job site, classically trained in Mechanical Engineering, 12 years as large commercial electrical design/builder, & 6 years inspecting The link is just something that I found on the net while looking for my own answers. I have no idea of its uses.

Now this is the type of discussion that I was hoping for. If nothing else, you gentleman are educating lowly engineers (like me) all of the world on the issues at hand. I do not see where anyone is being impolite. I was hoping that someone would look up the specs on their equipment. I do suspect that it is good for some types of refrigerants such as R427A but not necessarily for R410. Some refrigerants only require 95% pure new oil and they are fine. Apparently R410 is not fine with any residual oil. Once again though, I am just an engineer. I defer to the experts who have real field experience.

As I said, that was not for R410A - it was for other refrigerants such as R427A. I saw no such reference for R410A - but that is why I asked. Thanks for the clarification. So the coils will hold the pressure? I know that I am being the devils advocate here but I like to have all of the details and make my own informed decisions on a case by case basis because there are a lot of very different cases out there. PS. Love the Mongo... Soo Cool.[:-thumbu]

I have read just now on a few sites about the increased pressure. Is there any problem with the pressure in the old coils that could cause rupture because of a thinner wall? On the oil... I have just seen a few sites that mention draining the oil, adding new oil, putting the reclaimed r-22 back in - running for a while, removing the R22, checking oil properties with a test, and repeating until the % of old oil is tolerable then changing nameplate data. That is typically for different types of replacement refrigerant from R410 though. What do you guys think about these issues?

Did they mention how nice it was to have warm clothes to put on during those cold mornings.

There is a new mini-duct system... But I do not think that is it! http://southernmoheatandair.com/yahoo_s ... 32_std.jpg I must say that using a valve to divert the excess heat from the dryer to the adjacent space (such as a garage) in the winter may not be a bad way to go from an efficiency standpoint. I do not know what the code says about that though....[:-crazy]

If I replace an old R-22 condensing unit outside, do I really need to replace the entire inside fan coil unit? I am aware of the concerns for efficiency and variable speed; but I have some customers that will reject that and just say that they want to replace the outside unit and not the inside unit because they have 10 of them and they all have another 10 years of life. Realistically I see 20+ year old fan coil units every day. I would like to hear a few opinions on this issue as it is a rather large issue for the industry.

Trane is one of the better manufacturers for ease of finding data online If you searched google for trane ttn The first result is a pdf with all of the information on deciphering the Model Number. Trane always calls this "model number nomenclature" so you an always add this to the end of a search. Only enter the first 2 or 3 characters of the model number though...

Hello gents, I typically call for replacement of a pad mounted heat pump or condensing unit every 15 years - but I do not call for replacement of interior fan coil unit. Should I be calling for the replacement of the interior fan coil unit also - because of energy efficiency interactions?