HVAC Monitoring System - Buy?Make?

[pete_c]

Thanks Lou.

I remember making numerous excel spreadsheets with an accompanying logical drawing relating to the CFM / pressures etc to document said tweaking; for a kind of "as built" document for both maintainance and service of said system after completion (although I watched and learned the entire endeavor because I managed the implementation from "soup" to "nuts". At the conclusion the said endeavor I installed vendor provided monitoring devices which where built in and on the network. I pooled numerous of these devices such that I could manage and looking a more than one unit in more than one location. It was a learning experience.

 

[apostolakisl]

Here is what you need to monitor amps.

http://www.precicon.com.sg/Home/Monitoring/CurrentMonitoring/CurrentTransducers/tabid/914/Default.aspx

One of the models reads 0-10v. That would be perfect for the cai.

Maybe this model would be better.

http://www.veris.com/docs/Installs/h952_i0b2.pdf

The other one was $150, this one is $50

 

[etc6849]

This isn't related to automation, but has anyone looked into replacing an a-coil that has a static orifice with one having a TXV? My guess is this is where you can gain the most bang for your buck (I don't think it pays off to replace your entire system with a brand name system despite what most technicians may tell you).

The home I purchased last year was built in 2006 and has a cheap builder system. What I was thinking about doing was replacing the a-coils with new one's having built in thermostatic expansion valves (TXVs) to meter the refrigerant going to the evaporator via a mechanical diaphragm controlled by a mercury bulb that monitors the superheat. This should hopefully keep superheat constant over varying load conditions.

If anyone has done this type of modification to an older system, please reply with how much money was saved. Currently, I've gassed my units for the hottest day of the year using a superheat method (gauge pressures, temperatures at the air intakes, vents and ambient). If I go forward with my project, I would buy the parts myself (including a used recovery machine) and attempt things on my own. I'll also have to learn how to gas a TXV system (I think the method is slightly different as superheat is fixed).

I also agree that an inproperly gassed unit can cost you lots of money, and it would be nice to have some means to monitor this. The simplest approach is probably to add a sight glass to your system on the high side and look for bubbles periodically. It's also very easy to monitor how often you unit cycles on/off with most HA thermostats.

PS: The only "license" that is required that I know of is you have to pass an EPA test online and have some means of recovering the refrigerant. If you watch a few youtube videos and read a book on refrigeration, I think you'll know as much (or more) than the inexperienced tech that will be sent out to your house (unless you know of a skilled experienced technician and request him/her).

 

[apostolakisl]

This is the forum I have used when I have had questions like that. It seems odd to me that an AC unit wouldn't have a txv on it from 2006. Those things have been around a long long time.

http://hvac-talk.com/vbb/

You certainly can do all the work yourself without a license. . . if you can find someone to sell you the stuff. Most HVAC distributers won't even sell you a roll of duct tape without a license, and for sure they won't sell you refrigerant without a license (or anything that requires opening the system). A guy at our church has been telling me he has not been able to get his license despite a lot of course work, but I don't know, maybe he isn't very bright. He works in HVAC now under his companies license.

 

[etc6849]

You make a good point. Most of the guys who come out to your house really have no license other than an EPA certificate (that anyone can get online in a few hours, I don't really consider it a license, but you do need one to buy most refrigerants) as they work under the "supervision" of someone who holds a master's license that allows the business to operate in that particular county/region. These young unlicensed techs don't have the troubleshooting skills that someone who is logical and more experienced has. What's worse is they are usually afraid to ask someone for advice when they don't understand something. Further, they usually don't ask the why questions, so they will never be great technicians and fully understand things. I might be out of line, but I'll put my engineering degree and logical thinking up against any technician.

With regard to parts, I think you can always pay 15-20% above dealer cost and find everything you need online and be money ahead since most places charge 100% above their cost for parts. If you can't find the stuff you need online, just go and buy a used uniform and attach a label to it. I'm not saying it's the "right" thing to do, but no vendor is going to refuse a cash sale. You can also typically buy from most wholesalers if you're employer has an account there; just show the counter your work id. You can't or shouldn't use your employers charge account, but a vendor isn't going to refuse your cash if you have a valid id for company x and company x is in their system.

With regard to my out dated setup, I agree it is kind of crappy of a builder to install the bare minimum. However, if the buyer isn't smart enough to ask for something better, can you blame them? I didn't buy my home new thank goodness, but I've learned a ton from the last buyer’s mistakes. I bought my home as a foreclosure, so there is some truth to you get what you paid for. My home has been the only foreclosure in the neighborhood too, so hopefully things stay that way. Even though prices have continued to drop over the last year, I think I'm ahead versus renting the same style of home.

 

[apostolakisl]

I suppose it depends on where you go. Our local guys are very gunshy. Probably they got nailed at some point in the past. My friend used to own a hvac service company and he has a masters license. He sent me in to buy a compressor/evaporator for my wine room and they wouldn't sell it to me without actually getting him on the phone. And even then they were all grumpy about it.

And yes, the guys out there working under someone else's license may or may not have a clue (may not demonates). I have a strong background in physics and very much enjoy the subject. I find that following the logical process of cause and effect through a system can tell you a lot. But I have also found that you can't figure it all out just by looking at the thing and knowing some physics.

The HVAC forum I mentioned has some people that are knowledgable and willing to answer questions.

And yes, if you go online, you can pretty much buy anything no questions asked (except refridgerant). Our church had a compressor go out and was quoted $1500 to fix it. I bought a compressor online for $200 and the technician guy at my church installed it for free 4 years ago. That one is already a winner.

As far as hvac at your home. I know you don't want a new system, but if it is a builder grade deal, you probably have a crappy compressor, evaporator, and condensor. I have been very happy with my carrier infinity unit. It runs at 19 seer (they claim) and is dead silent. It works even when it is 107 outside. My parents just repalced their builder grade unit with one of those in their florida house and cut their electrical bill in half. The old unit was 12 years old.

 

[etc6849]

If I was going to stay in my home for the next 10-20 years it might be worth it. However, I know for sure I will have to move in 6 years as part of my job.

I'm also not so sure replacing a no brand unit that's five years old makes sense. I think if you install a TXV on an old system you should see some of the savings without the huge equipment expense and be better off over a 10 year period (money wise). Water cooling the condenser also sounds like a good idea to explore.

I could be wrong, but I don't think there's anything magic about Trane, Carrier and other name brands versus the cheaper no name builder's models... They all use components made by the same companies (tecumseh, copeland, ao smith etc...), even down to vital parts like the compressor. Of course, when comparing, you should compare units of similar efficiency.

 

[pete_c]

Personally I learned a bit about residential HVAC in the 80-90's. I did some computer work (custom billing database) for a local HVAC company.

By the late 1990's I became a bit self sufficient relating to my zoned system in my old home. Today if I can't figure out an issue I talk to the HVAC guru at the same HVAC company. He's close to about 60 now and has been a right hand to the company since he was about 19. He is very good at what he does.

The last endeavor in the current home was replacing the blower motor on my furnace. I was upset about it because the furnace was less than 4 years old and a sticker on the furnace indicated that it had been replaced about one year after installation.

Diagnostics were basic. The motor replacement was time consuming but not difficult. The cost of the new blower motor was neglible. Its been a few years now and the furnace is running fine.

Relating to the OP; with the advent of what you can do with HA and how knowledgeable you are with HVAC you can do much. Monitoring your furnace run times, HVAC times, etc is really just the tip of the iceberg relating to what you can do with HA.

 

[apostolakisl]

I just don't get how your ac unit doesn't have a txv. Is it just fixed orifice metering? Even my car doesn't have that (it has a big/small orifice metering). I spent about $30 for the txv in my wine room. Admittedly, that is only a 1/4 hp system so a bigger models probably are more, but they still aren't that much money relative to the system cost, and without it, I just don't see how it would meter for crap.

 

[KeepItSimpleStupid]

My $.02

In reality, you need to be able to caclulate superheat and subcooling. See: http://www.ehow.com/how_5410905_calculate-subcooling.html for the sub-cooling calculations.

For quick and dirty checks, you need to look at the temperature and humidity of the air before the evaporator and the temperature afterwards. A range of temperature drops decreasing with less humid air is a worthwhile guage, but it should be done at a specific fan speed.

Carrier does some sort of wierdness. The motor controls can effectively determine static pressure indirectly by measuring the current drawn and the RPM of the motor. I do think that really humid air can confuse the filter monitoring software, but that's just my opinion.

The carrier Infinity systems every day at 1:00 PM, it runs the blower on MAX and opens all of the ducts to max if you have a zoned system. I believe, it's trying to determine the % change in static pressure since the filter was changed.

So, CFM and static pressure and CFM measured under specific conditions (All vents open) makes sense to determine if there is a filter issue especially if you have something to compare it too.

If you want, you could include a compressor power sensor, but you need to be able to effectivlely be able to measure efficiency. Energy in in vs BTU out. That could get messy.

The nost important quick and dirty parameters are:
1. temp/humidity before evaporator
2. Temperature after
3. pressure drop across the filter.
4. Air flow in CFM

 

[ronaldbroth]

There is a company that makes a nice delta T monitoring system for HVAC Monitoring and Diagnostics. Web site is www.mHVACmonitor.com