I was looking to beef up my offerings for standard energy audit and feel like some quick screening tests for HVAC would be great. The only test I currently do is a dominate duct test.
Since I am lacking on the HVAC knowledge side, I would also like to know how to interpret those tests - I am sure someone will suggest a static pressure test - so, how do you perform and what is normal and what actions do you recommend for results outside of normal.
Do a true duct leakage test, dominant is pretty worthless
Do not do a static pressure until you learn from an HVAC guy, as all it takes is one mis-drilled hole & you just bought a whole new unit
The test is quite easy & you simply compare that number to what is listed on the plate - if it is over you have issues, as for the fix it depends on what the real issue is
Best blog I recommend for reading up on this: http://ncidavid.blogspot.com/ including how to do it, etc...
Great blog - thanks for the heads up. I do duct leakage testing...dominant just to see if the house is being pressurized or depressurized by the unit.
Craig, do you typically see heat pumps, gas furnaces, A/C only, or what?
All of the above. I am not too concerned about furnaces since our heating load is so low here in Tucson, AZ. I am mostly interested in heat pump and AC tests that do not take long to perform and will uncover red flags that may require more testing to fully evaluate. We do have a lot of heatpacks, and I assume there are not a lot of tests I can do with those.
We have a lot of heat pumps here, but there are often control issues so that the heat is coming from heat strips, even in mild weather, and the heat pump is not running. I have also seen the fan running but not the compressor. So, quick checks with the IR camera (looking at the refrigerant lines), or even just touching them with fingers, and a current clamp in the electrical panel, tell you something about how the system is operating.
Other than that, a duct blaster test and an airflow measurement are very useful. The duct blaster takes some time to set up, the airflow takes less, they both take $$ equipment. I agree with Sean that you should be careful if you drill holes in equipment, but if you figure out how to do it you have another measurement.
I would suggest going to TruTechTools.com and look at the trainings they have recorded. The trainings are great for getting a grasp on how to take the measurements as well as what to look for. With a little training and the right tools you can actually calculate real time system capacity for your clients.
Static pressure is a great test, but I agree with Sean - you need to find someone who is knowledgeable to teach you how to do it and what the results can indicate. You can measure static across several points in the system to help narrow down potential issues, but in the end, you will still need a good HVAC contractor who understands system design and construction to identify the specific issues and solutions. A duct loss test (duct blaster) combined with use of a flow hood can also be very instructive - as this is a primary cause of a lot of energy loss, infiltration and comfort problems in many homes.
You can also consider performing a Manual J heat load calculation - there is plenty of software available to do this (even apps for the ipad). This will help you to determine if equipment is mis-sized. (Heat pumps will also need a balance point calculated along with an airflow evaluation - but a load calculation will give you a good indication of potential issues). Mis-sizing of equipment, even furnaces in Tuscon, can lead to significant comfort issues, and cause equipment to fail prematurely. Again, partnering with a good HVAC contractor who can evaluate and solve any potential issues you find is recommended. Check out the video "Bigger is Not Better" at http://www.belred.com/products-solutions/videos for more information on load calculations and HVAC equipment sizing.
To see what services we include in our home audits (and maybe get some ideas for yourself) check out http://belredhomeenergy.com/assessments.
One to the easiest tests you can do is to measure the temperature drop across the a/c evaporator coil or the temperature rise across the heat exchanger of a furnace or on a heat pump. All you need is an HVAC thermometer. When in a/c mode (for either an a/c or a heat pump) let the unit run for ten minutes and measure the difference between the return air temperature and the temperature in the supply plenum and you should get between 17F and 21F. Return air is 75F the supply air should be around 55F. If it is say, 11F, then you have a real problem like an iced up coil, or way too high airflow. If the difference is too high like 24F, then you again could have a refrigerant leak or low airflow caused by a dirty filter or a dirty evaporator coil.
When in heating mode for a gas furnace you should see a temperature rise of between 35F and 60F on most units. High efficiency units tend to be on the low side of this range at 40-55F temperature rise. The allowable temperature rise should be stated on the name plate or in the operations manual. Say, 70F return air and 105-125F supply air temperature. if it is higher than this you are too hot and the unit may shut down on a high heat overload safety cutoff before it satisfies the thermostat. You also may have a low fan speed and are not moving enough air over the heat exchanger. If you temperature differential (Delta T as engineers call it) is too low, then you may be under firing the unit or the fan speed is too high any you are moving too much air over the heat exchanger.
On a heat pump in heating mode, you should see between 25F and 35F temperature rise depending on outdoor temperature. With a heat pump you don't have as much certainty about temperature rise since it goes down as the outdoor temperature goes down.
Great recommendation. I would add that radiant heat from a hot heat exhanger can skew the temperature reading if the heat exchanger can "see" your probe. Move around the corner a couple of inches into the trunk and make sure your probe is in the flow, not at the edges.
With a flow hood, take a round of readings and forget the Manual J for a minute. Look at the relative amounts of air moving. As an example, does each of the bedrooms have the same amount of supply? Does the master suite have it's proportion when you look its bedroom, bathroom, toilet room and closets vs it's floor area? Is the master bath over a garage and therefore needing a little extra (ignoring for now the many thermal problems that happen with the room over garage)? You can learn a lot by just thinking about those readings.
One of the main problems we see in houses from '95 on is the attic system in a 3000 ft2 2 story has its thermostat in the master BR and that room typically has too much total supply, so the other rooms on the second floor don't condition as well.
Rule of thumb, we want 60% of the cooling air to get to the second floor, and 60% of the heating air on the first floor, if the 2 floors are the same size.
Rule of thumb, we want about 80 square inches of supply and return trunk per ton, so you can make a quick measurement of the total trunk size, and see if the "left" trunk and the "right" trunk are about right
Rule of thumb, each ton of A/C wants to move 400 CFM. And in your climate, y9u can get a sense of how many ft2 of house each ton will serve. In my mid-Atlantic market, a 1990 house of average configuration needs a ton for every 5-600 ft2. An energy star house needs 700 ft2 per ton, whereas the 2012 IECC houses we see are about 900 ft per ton. My HERS 42 house has 1100 ft2 per ton and it is a bit too big - should have been 1300. Rule of thumb only - odd shaped houses are not rule of thumb houses.
Another quick one, since you have a flow hood, is to take a flow reading of a typical register with a flow hood - an anemometer set on top of the register would also be acceptable. Turn the fan switch to "ON" and take a reading. Remove the blower cabinet door and tape the cut-off switch, turn on the fan again and take a reading.
If the flow hood shows more than about a 10% increase, you probably have restricted return, common in our area of the mid-Atlantic. I have seen a 100% increase. Be sure the filter is clean before this test. I am not sure how to relate differences with the anemometer, but a large increase in flow would also be indicative of too little return.
If you are getting into duct diagnostics, then a thermometer with a longer probe and a flow hood are the first 2 purchases.
Great responses, I will have to digest for a few days!
I look at David Richardson as a great mentor. And Sean does make some fantastic contributions. But my love of sparing with Sean forced me to attempt to one up his link share, and I think I may have it.
Here's a great VIDEO by Jim Bergman of how to do ESP: http://bit.ly/trutechESPdrill