So the other day a gentleman and I were visiting, and we agreed that a key value of preventative maintenance for HVAC systems is avoidance of future costly repair bills.  No argument here - I think everyone agrees.

Then he asks, is there operational costs value (reduction) to preventative maintenance?  Make it as simple as changing a filter every X (6 for me) months.

The kicker was, he says to me, by the way, you've got this fancy energy monitoring system that's customized for geothermal heating/cooling system - if there's operational costs benefit to routine maintenance, I should be able to quantify it.

Well, I certainly believe there's operational costs benefit to routine maintenance, like regularly changing a filter, cleaning evap coils, etc., but I didn't have the data.  So I accepted the challenge to show quantifiably that indeed there is benefit, knowing I have plenty of data to analyze and prove things from.

This is turning out to be a more difficult assignment than I thought.  So far, I can't produce the numbers to quantify something like, for me, changing a filter after 6 months.

I first thought that run times would be improved (less).  But outside temp variability (degree days) causes way too much 'noise.'  Same for power consumption measurement specific to the HVAC.

So then I looked at KBTU/hr, thinking that efficiency would suffer as a filter gets dirty.  Can't see it, though.  And I think it's because KTBU/hr efficiency doesn't have a power or energy component to it.  As the filter gets dirty it may take more power due to higher ESP, but that's not going to show up in my Heat Extraction KBTU/hr measurements.

So then there's COP, which I also measure.  Surely this would show the benefit of a filter change, without being influenced by degree days.  But, can't see it.  I changed my filter on Jan. 4th, and my COP values didn't budge (stayed steady before and after).

So I ask all of you, what are your thoughts?  Where should I be able see operational quantifiable benefit of something as simple as changing the filter? or like cleaning the evap coils?

Keep in mind I have an ECM2 fan motor, and I almost always run in 1st stage, if these make a difference (WaterFurnace Envision GSHP units).

Many thanks!

Best regards,

Bill

I suspect it would take a very heavy coating of dirt before the reduced heat transfer and decreased efficiency measurements would punch through the noise of daily variations in weather. Outdoor temp is a primary driver of load, but secondary factors such as wind and sun have an influence.

Nearly all airfilters leak owing to loose fit, unsmooth edges of filter and rack, etc. A dirtier filter may increase blowby, causing the evap to get dirty. Getting an evap truly clean is hard without removing it, an expensive proposition.

Curt,
Good points. I have had some real time experience with a dirty coil. My filter was slightly undersized which resulted in clogging the evap coil. I didn't notice this until I started to get blowback from my ecm blower motor (it literally sucked the water off the evap coil). I had my HVAC guy cutout a section of the return near the coil (for future cleaning) and put in an access door. This did not cost me much (hence the value of maintenance) but could have if not detected right away.

My brother has an EarthLinked DX heat pump in his home. He has admitted many times forgetting to change the filter. The thing that reminds him to do so is the power bill has gone up higher than expected. I don't know, though, how you would quantify it with your monitoring system...

Thank you for the comments.

I think that COP is the only measurement (I can think of) that is not generally affected by day-to-day degree-day changes.  Or perhaps my GSHP units are too new (2.5 yrs) and/or I don't let the filters get dirty enough to see measureable impact to operational performance.

I'm working a project at the moment where I'm trying to quantify the benefits of routine and/or preventative maintenance with respect to daily operational performance.  If anyone has a quantifyable example they'd like to share, I'd sure appreciate it.

Many thanks.

Best regards,

Bill

I think this is kind of like changing the oil in your car. You don't expect to see better gas mileage, but you know that your car will last longer if you do regular maintenance.

Air filters are both very important and often sorely neglected. I'd like to see systems more emphatically annunciate the need for change. Some thermostats incorporate a filter reminder, but I'm not sure too many folks pay attention. I haven't run too many service calls, but a majority of them include or stem from a horribly clogged filter.

Bill I think unless you let your filter go a year or maybe 18 months you won't see it. Maybe try extending out the filter changes until you notice a change in COP on the change. That will also tell you you're at the point it really matters to change a filter. With the ECM I bet it will slowly increase the fan speed to make up for a dirty filter, but at some point it will hit a wall.

Having worked a lot with water filters I can say they actually filter better as they get dirty until the point they don't pass enough water. So changing them to often actually lets more "dirt" pass. I would assume air filters are similar?

For our first year our fan ran any time we were off peak or about 14 hours a day and all weekend. I have since switched to letting it only run when the heat is called for to reduce electrical consumption and heat usage since it would move heat to places that weren't calling for heat (3 zones). This has saved energy, but I am noticing more dust build up and a much longer filter change time. I have a magnehelic gauge on the blower and just change it when it moves from .15 to .20 with the blower on low speed. I had been changing the pre filter almost monthly and now it has been over 4 month and I am at .19.

Gentlemen, thank you for the comments.

I agree on filter change not (materially) affecting operating values unless filter condition gets to be catastrophic.  With my GSHP units, for example, as clean as they are being only 2.5 years old, I'm sure operating values such as power and COP are affected as the filter gets dirty, but they're not measurable within normal usage.  And weather pattern certainly will overshadow being able to see any power increased requirements.

I too have a magnahelic gage on my filter.  I used to change my filters based on increased ESP reading - i.e., when the pressure got to a certain point I'd change a filter.

After a while of changing filters, I noticed I was going at least 6 months between filter changes (I have very large surface area pleated filters on my units).  So now I simply change the filters on a 6 month interval basis - much easier to remember to do than going up in an attic and checking a magnahelic pressure reading.

My question to all of you is, are you aware of a magnahelic/ESP style instrument/sensor that has some kind of a digital switch output that closes/opens based on reaching a certain ESP?  I could connect something like this to my energy monitoring system to then signal to me it's time to change a filter, all without having to constantly check a gage.

Many thanks.

Best regards,

Bill

 

 

Dwyer is making some with remote switching and remote view. At work we are contemplating getting some to send signals when they need to be changed rather than changing on fixed intervals. I haven't seen a price, but they are probably not cheap.  Fortunately mine is in my shop where I see it almost daily.

http://www.dwyer-inst.com/

I think the true value of maintenance is that it keeps us men away from our wives long enough to provide small breaks between putting our foot in our mouths.

I wonder if UHaul, Penske or FedEx would have some insight on how to quanitfy benefits for their large vehicle fleets that could be applied to GSHPs?

My mother-in-law made a comment today that her cooling bill was $600 last month, our cooling bill was $165 for the same month. Now it's been pretty warm here, in fact the last 2 weeks there been a heat wave in the north east where temperatures were in the 90's. But $600 for a house that has two geothermal units is excessive. When I got home, I rushed to check our energy usage thus far for the month, and came up with 1200 Kwh, about $190 for 3 weeks of cooling. My in laws house is actually smaller than my house, the 12 foot ceilings they have I'm sure have some impact, but I can't see it being that big. Anyway, I'm thinking the difference is dirty air filters, I plan to check them tomorrow, is there any other neglected maintenance issues I should be looking for when I check the air filters?

> digital switch output that closes/opens based on reaching a certain ESP

You can use a two port pressure sensor for an analog output.

http://sensing.honeywell.com/index.cfm?Ne=2308&ci_id=154348&N=3383&la_id=1

That's pretty extreme based on your description. This heat wave has been tough, and we've had double the cooling requirements (here in Eastern PA) compared to last year.

Are you sure it's their cooling bill? Is that a disaggregated number of just their total electric bill? Do they have a pool? How about dehumidifiers or any other energy hogs?

A professional energy audit would probably pay for itself quickly. You need to attack this in a methodical fashion and get it figured out ASAP. It could be something as dumb as a duct has become detached in their attic and the system is sucking 150F attic air into the return. I see this a lot.

A qualified person can check air filter, coil and blower cleanliness, unit status lights, thermostat for error codes/lockout alerts, EWT, LWT, loop pressure, gpm, air delta-T, DSH operation, look for nasty things growing in drain pan that may clog condensate line, amp readings on blower, heat strips, (I'm not sure if our installer checked compressor amps), calculate heat of extraction/rejection. What did I forget?

If the buffer tank is wired, make sure the circuit breaker is off unless there is a reason it should be on (Ex. extra hot water needed for guests.)

Some more questionable items to improve life: motor soft start, surge suppressor, low voltage cutoff, thermal cutoffs, minimizing cycling.

Posted By tinoue on 09 Jul 2010 07:23 AM
That's pretty extreme based on your description. This heat wave has been tough, and we've had double the cooling requirements (here in Eastern PA) compared to last year.

Are you sure it's their cooling bill? Is that a disaggregated number of just their total electric bill? Do they have a pool? How about dehumidifiers or any other energy hogs?

A professional energy audit would probably pay for itself quickly. You need to attack this in a methodical fashion and get it figured out ASAP. It could be something as dumb as a duct has become detached in their attic and the system is sucking 150F attic air into the return. I see this a lot.

The bill is there overall electricity usage for the house.  They do have 2 refrigerators and the sprinkler system is on the well, instead of city water, but i can't think of any other energy hogs they have in the house that could account for such figures. They do a lot of cooking with electric stoves, but no more than they normally cook other parts of the year. Since cold air falls, I wouldn't expect there 12 foot ceilings to have much of an impact. The other half of the house, where the bedrooms are have normal ceiling heights. There system is split into two zones, two Florida Heat pumps, one for the bedrooms and one for the living areas. I wouldn't expect any duct work to be in the attic, since both heat pumps are in the basement, and they have no second floor.  I'm sure replacing the filters will have some positive results, but they may still benefit from a home energy audit.

  

I wonder if an electrician can narrow down the problem by checking electricity usage on each circuit? Was the electricity bill actual, or estimated for the past few months? Is this a catch-up bill from a budget payment plan?  I'd start with the paper bill itself to see what information it can tell you (if anything).

It sounds like there's something mysterious going on. In situations like this, if nothing is obvious, I resort to using a clamp-on amp meter, and go through the circuit box, breaker by breaker, looking for large loads - not recommended for the casual trouble-shooter due to the potential for electrocution....

There's some additional simple troubleshooting you could do. On a hot day, note the outdoor temperature and set the indoor temperature/thermostat setting. For a couple hours, time how long each system is on vs. off. You want to time it long enough that you get maybe 5-10 on/off cycles. You also want to ensure that the thermostat has been on a constant temperature setting all day so that it's not giving you false figures.

By doing this, you can start to sanity check the system. For every ton of capacity, running for one hour, the system will use approximately one kwh of electricity. You can also review their electric bill during the spring when they weren't using heating or cooling, to get an idea of the loads that weren't taken by the HVAC system. With a little number crunching, you can determine if the numbers make sense or are way out of whack.