Heat Strip Sizing and Application | HVAC Training

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This video is brought to you by navac Empowering you to work smarter with Their new Break Free power tube expander The nte 11l So in this section we're going to talk About overcoming defrost and when I talk About overcoming defrost we're talking About a heat pump cycle in which you Have the machine go into a defrost cycle And heat strips coming on to counteract The cooling process so to explain it for Those who are unfamiliar with heat pumps Are new to the trade when a heat pump Goes into defrost the HVAC system Switches from heating to cooling the Reason why it switches to cooling is Because it wants to warm the outdoor Coil and when it warms the outdoor coil Any Frost and Ice that have accumulated Will hopefully melt off during the cycle It runs between just a few seconds all The way up to 10 minutes A lot of times They term in it at 10 minutes as a Maximum run time And typically that's sufficient for Every defrost process there are certain Times where there's an ice buildup or an Ice storm where you'll have a problem With defrost where ice will accumulate It'll either lock up the outdoor fan or Just cover the coil in a way that the Defrost cycle can't melt like it's Separate from the coil but it's still Shielding the airflow from coming across

The coil So when that system switches into Cooling obviously we're in a heating Cycle so it's winter time fall early Spring it's cool outside So when it switches into cooling the House is obviously not wanting to be Cooler it's wanting to be warmer so you Had to have a way of reversing that Cooling effect that's when the heat Strips that are on the inside air Handler Will come on heat strips are just Resistive Heat That is just like a mobile home electric Furnace it's just a small compartment Typically an add-on to an air handler or There's a whole kit you can put on Separately sometimes but most of the Time it's just a provision or a part That's put into a slot on an air handler That's made for heat strips and they Typically come in a few sizes they go All the way down to I know I've used 3 KW before all the way up to commercial Sizes of The maximum I've used is I think 25 KW But they go higher than that and they go Into three phase 460 all the different Voltages you might be familiar with as a Commercial technician But for the most part residential you're Talking about 208 230 and you're talking About

5 KW 10 KW 15 KW or 20 kW with some Variations like seven and a half or Eight and sometimes a three three is Pretty uncommon I only did that once or Twice So these heat strips will produce heat To offset the cooling effect that Happens now what we're going to look at Is we're going to look at how much Resistant heat do you need to offset That cooling effect and we're gonna have To draw some conclusions based on a Chart and we're going to be asked to Make some assumptions which is dangerous But the idea is to kind of understand What you need to do when you're Installing heat pumps in whatever Environment that you're in so we're Going to go to a cooling chart that's on A Goodman gsz I think it's a 15 Seer Three ton unit and we're going to take a Look and see what the cooling chart says At the minimum temperature they list This is our cooling data for a g s z H5036 a three ton heat pump 15 seer and This particular chart is matched up with An AM St42c it says So it has an outdoor temperature listed Across the top that ranges from 65 Degrees to 115 you have indoor dry bulb Temperatures on the left side of this Chart you have various airflows you can Choose since it's three times we're

Going to choose 1200 we're going to Choose that nominal 400 CFM per ton and Let's take a closer look at the 65 Degree section that's the lowest outdoor Temperature they list for cooling at 65 Degrees they have an indoor entering wet Bulb temperature range they have 59 63 67 and 71. so what we're going to choose And 71 isn't even listed on the 65 Degree side so we'll go with the lowest Indoor wet Bowl because we're going to Be talking about wintertime usage that's 59. so a 1200 our MBH is 36.4 so 59 Degrees indoor wet bulb 1200 CFM we have An MBH of 36.4 so that's pretty much our Full capacity right there for a three Ton unit 36 000 BTUs and as it gets Hotter outside you can see that Diminishes a little bit when it gets up To let me look at 115 just as a Comparison since we're looking at this When we get up to 115 we have a 29.8 so It's not substantially lower it's not as Steep a drop off as our heating data was For a single stage Goodman unit so if we Were to go down to 35 degrees Fahrenheit That would assuredly drop off some but We don't know exactly how much it would Drop off so let's say it dropped off We'll make an assumption and perhaps Some of you can chime in on your Experience with this let's say it drops Off to And even thirty thousand two and a half

Tons of cooling so at thirty thousand We need to be able to overcome that Amount of cooling with our heat strips It doesn't necessarily have to heat the Room it just has to offset that Particular range of cooling So let's take a look at heat strips and See what we're going to be able to do With our heat strips and how many amps It's going to take because that's going To be a factor as well As you see we're now looking at a Goodman air conditioning heating hkr hka Hkp and HKS electric heat kit for air Handlers and packaging electric units Specification sheet so we're going to Get to a list of the specifications for Various sizes and compare them as many Of you will know the aruf air handler is One of the most common Goodman Air Handlers used it's their Base air Handler AR U is unpainted and F is flow Rater meaning used as a piston So it's pretty common especially in Budget applications like builders If we look at the aruf 18 right off the Bat they have a range of heaters from 3 KW to 10 KW if we scroll all the way Down to the aruf let's see what the 60 Says Aruf60 says all the way from 3 to 25 KW And you see there's a lot more Information for the 25 kW to 20kw and The 15 KW and I'll tell you why that is

In just a minute So let's go back to the aruf 18. we see There's an hks03 3kw Hks05 Hks06 Hks08 and HKS 10. And we go to Circuit one because this Particular heater only has one circuit Because it's so small The threes to tens are relatively small Heaters and we see the First Column is Heater and amps You see there's two different numbers 10.8 12.5 it's the same way with the MCA Which is minimum circuit ampacity and Mop which is maximum over current Protection You'll see two different numbers Because this air handler can be used With a 208 voltage or 230 voltage range There's two different numbers for each One of those voltage range one on the Left for 208 one on the right for 230. So you see the heater amps will vary Based on which application it's in so Let's take the most common that I would Have seen is 230 and we have an hks-05 Hks05 will have 20 amps at 230. The minimum circuit ampacity is 27 and What that means is you have to have a Wire that can handle that minimum Circuit ampacity has to be 27 amps Typically people run 10 gauge wire for This as long as it's a proper wiring

There's about a million different kinds Of wires out there so you'll have to Rely on your electrical ability to know Which wire it is I can't get into all The different wires but there's certain Ones that are fine and certain ones you Cannot use For mop maximum over current protection It is 25 for the 208 and 30. for the 230 So it sees a little bit more than the Minimum circuit ampacity so if we know That it's going to run 17.3 amps for 208 or 20 amps for 230 we Can make some assumptions 20 amps times 230 volts is 4600 Watts so to understand how much Heat this thing puts out we have to know The formula for converting watts into BTUs this is on a website called Unitconverters.net I'm not affiliated With this website this is just something I found with a Google Search and it's Going to show us how many BTUs Our heater is going to put out with the Wattage that is running Now to convert watts to BTUs you just Multiply the Watts times 3.41 so we're going to type in our 4600 Watts and then we get 15 695 BTUs per hour if we have an 18 000 BTU system 15 695 will be a little bit shy if it's

Warmer but as it cools off that's going To be an appropriately sized heat kit It'll be close to breaking even but Appropriately sized so what happens if We go up to a 10 KW heat kit making the Assumption that we're just going to Double our 4600 number since it's a 5 KW We're going to go up to 10 KW we'll just Double this number and put 9 200. that Puts us at 31 391. At that point we're above two and a half Tons so we have more than enough where If the heat kit comes on it's actually Going to be heating the house somewhat Giving it probably the neighborhood of 10 to 15 000 BTUs Which way do you go well there's a Maximum heat size you can use for each Air handler so you can't go in excess of A certain amount With air handlers you have to stay Within the spec for what their airflow Capability is meaning you can't put in So much heat that there's not enough Airflow to dissipate enough of it it Won't go off on limit or be dangerous to The components or the duct work where it Could start a fire so with this 18 000 BTU air handler you're looking at 10 KW That's the maximum you can have and at 10 KW looks like you're going to be Putting some heating into the home During a defrost cycle whereas with a 5kw you're going to be breaking even

Now there is some energy usage there but Also there's energy loss where if you're Cooling a home slightly or you're Braking even as opposed to heating it You'll have to continue to heat it back Up once you're done so it's kind of a Gray area I think in my personal opinion You could use anything from breaking Even to slightly warming the home in Order to stay efficient you guys chime In on what you think but that's just a Look at the 18 000 BTU air handler let's Go back and look at the 36 000 which is Probably a little bit more common Because that's an average size unit so At 36 000 let's say it drops down to 30 000 at really cold temperatures when We're running into defrost let's see What our heat kits can do then we know What 10 KW produces right over thirty Thousand so we'd be right at the Breaking even point but what if we Wanted to have a slight bit of heating What if we tried the 15 KW what would That do so if we have 9 200 Watts Because we increased by 4 600 to get to 10 KW we have to add 4 600 more which Will put us at 13 800. so let's type That in and see what it says At 13 800 watts we have 47 087 almost four tons of heating so it's Going to give us between a ton and a ton And a half of heating during the defrost Cycle

And now let's go back to our unit charts To see what it says about how much Heating you can put in one of these Three ton units so with the aruf 36C Which is our midsize cabinet aruf air Handler you can go all the way up to an HKS sc20xf Which is a 20 kW two circuit heat strip Very interesting see there's various Heat strips here there's a lot of Choices but it ranges on 36 from three All the way to 20. so you have to check The specs to make sure you can do it and When you're setting up the blower you Have to make sure that you design the Airflow so that it can still tolerate This heater you can have an air handler Capable of running 15 20 25 KW but if The blower is not set up properly it Will be incapable of dealing with that For example if you have a five ton air Handler and you want to run 25 KW but You set it on low where there's a decent Amount of static pressure still it may Be incapable of producing enough airflow So you have to confirm the airflow Amount or test the static pressure to Confirm your airflow before Finalizing that heat strip check because If it doesn't have sufficient airflow You could be in danger of fire melting Or just intermittent operation and early Failure on a various array of components And to wrap this up remember what

Voltage you're running when you check These charts because the performance of Any machine is going to vary based on The voltage you may have 208 single Phase you may have 230 you may have Three phase as you go up to commercial In various sizes there's a few homes That have three phase I've never been to One personally but I've seen them I've Watched YouTube videos where some of you Guys have gone to homes with three phase I've never seen that before I don't know how that happens I'm Guessing that's a rezoned home issue I'm Not sure But just make sure you verify what the Electrical situation is then you can go To the chart and you can make sure you Have the right heat strip because the One thing you want to avoid is putting In a heat strip that's insufficient Even if you're lacking an amperage and That's going to be one of the big things That happens you're going to get to a Home where they have insufficient Amperage Maybe they have a service an old Electrical service it's 100 amps and They can't tolerate because let's say They want to heat pump because some People do that I had a customer one time Who was afraid of gas and had to have a Non-gas appliance the house was old 100 Amp service so if you run a three ton

Unit because if the house is old chances Are it's going to need a decent amount Of heating as well If you run a three ton unit or even a Four ton unit let's say and you can only Put in 5 KW well that's gonna be Insufficient to overcome defrost and During a defrost cycle you're going to Be cooling the house off because Remember in the heat cycle you're Battling against heat transmitting Through the walls to the cold climate Outside And the cooling cycle in a cold climate There's no battle going on so it's going To be straight up rapid cooling inside Depending on how much your heat strips Are lacking Keep that in mind At the very least you need to have a Long conversation with a homeowner about The effects so you can avoid any Liability and get them to sign something Because it'll come back to bite you in The buttocks whenever they're going Through defrost and saying it's blowing Cold air all over them it's Uncomfortable you can say here's the Paper you signed You said you understood I am sorry we Can go back and upgrade the service Which a lot of times is what I see Happening when you go to a house where There's 100 amp service it's typically

Time to get a 200 amp service for that House and they have to go through that As well and if they're going through the Process of buying a new HVAC unit they Should probably also go through the Process of upgrading the electrical to Suit the proper HVAC unit Sometimes people can't do that maybe it Look at the mini split option maybe That'll run a little bit less Electricity no heat strips there might Be a better option try to think outside The box or convince them that gas is Okay which I think gas is okay I'm okay With gas we're out in the uh country we Use a French fuel called propane and It's not cheap but it does the job and Sometimes you have to use it for lack of Options if anyone needs any Clarification on this just let me know You can always email me at hvacshoptalk Gmail.com and we'll talk a little bit More about this heat strip stuff in the Future as well

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