Soft start needed for new heat pump?

Ghcoupons

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Congratulations on your efforts. The size of a system may have to do with the Net Energy Metering plan your utility provides. You may want to oversize because no matter how good the NEM plan is today, it will most likely get eroded as time periods change and fixed charges creep into the rate structure. The good new is that costs continue to come down. I just saw a generic Tesla proposal for $2.00 per Watt in California.
What I would love to see in my lifetime, is a legit way to be off grid with power to spare at an affordable price. Solar all day, batteries all night, even with heat or AC and not pay 50 grand for it.
 

Ampster

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What I would love to see in my lifetime, is a legit way to be off grid with power to spare at an affordable price. Solar all day, batteries all night, even with heat or AC and not pay 50 grand for it.
I am working on a variation of that. We are looking for a house with a little acreage nearby and even though it will most likely have a grid supply I hope to be self sufficient and only need the grid for backup. I will probably still charge my EVs from the grid but that will probably be less expensive than the equipment needed to do that. Having a grid connection will allow me to get one of those cookie cutter GT Tesla systems for about $2 per Watt. I have the inverter and the battery storage but the wrinkle is if I can get it installed and approved before the new NEC 2020 code requires UL approved battery storage.
 

Hedges

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A grid tied system that will allow me access to The power when the grid is down, even just when the sun is shining is my goal, with the hope to add batteries sometime in the future.

A batteries-optional grid interactive inverter may be ideal. I think there are some brands.

SMA Sunny Boy grid-tied inverter has "secure power", a PV-only powered 2000W outlet that works during grid failures when the sun shines. Have to see what the present situation is with "Rapid Shutdown", if that feature still prevents "secure power" from working. They have a couple different battery inverters which can be added later to make a complete backup system.

Yes, it’s pretty straightforward. They buy wholesale. They encouraged me not to look at it as a revenue source and shoot for but not go over 95-100% of the power we need. That is my goal anyways. A small or non existent power bill would be great, but self sufficiency is more my main goal.

I think you can put in DIY grid-tie PV for under $0.05/kWh (amortized over 10 years) including mounting racks and electrical stuff.
If buying power costs you $0.20, then aiming a bit over 100% to avoid every buying power from them for 4x your self-made power could be a good tradeoff.

If they buy a kWh from you during the day for $0.04 an sell it back to you at night for $0.20, it's hard to match your consumption to production. So long as you get net metering, and they buy surplus remaining end of the year for wholesale, then go for it. We used to lose surplus at annual "true-up" but now get paid $0.04/kWh. Our time-of-use schedule has changed to less favorable in some ways but better in others.
 

Ghcoupons

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I am working on a variation of that. We are looking for a house with a little acreage nearby and even though it will most likely have a grid supply I hope to be self sufficient and only need the grid for backup. I will probably still charge my EVs from the grid but that will probably be less expensive than the equipment needed to do that. Having a grid connection will allow me to get one of those cookie cutter GT Tesla systems for about $2 per Watt. I have the inverter and the battery storage but the wrinkle is if I can get it installed and approved before the new NEC 2020 code requires UL approved battery storage.
It’s funny, with so many options out there, Tesla keeps popping up. I can’t figure out if it’s just because they’re the “golden child” right now, they’re truly a quality product, or some mixture of both. I wouldn’t mind having some power walls but I don’t like some random company , thousands of miles away having control over my system.
 

Ampster

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Tesla keeps popping up. I can’t figure out if.........
They have changed their philosophy from the days of Solar City. They are offering cookie cutter deals and very low prices. I drive two of their cars so they are not some random company to me. I do not expect much service for that price and would hedge my bets. I can tackle a lot of DIY projects but at my age, not ones on roofs.
 

TKB4

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To original poster. I have a 3 ton inverter heat pump that varies from30% to 130 % of 3 ton rating its a nordyne unit renamed for maytag taipan and Fridgidair among others mine is 21 or 22 seer and max draw is 11.9 amps and it ramps up slowly never going over this 11.9 amps. It also has dual fuel with gas backup. I also have a climate master tranquility geothermal open loop system that is 2 stage with a scroll compressor and soft start grundfus well pump. The 2 stage units typically ron at about 60% of rated tonnage or full rated tonnage and start with stage1 then later progress to stage 2 if needed. I have no trouble starting the inverter unit with a 5,000 watt inverter. I am currently looking at 13,000 watt inverter and using a sure-start soft starter which should reduce the LRA of 150 on my 5 ton unit to about 44 amps or less.

Other suggestions for saving power and loads are a heat pump type dryer that generally uses about 450 watts and not all even require a vent. Also a heat pump or direct PV water heater or preheater. I use a PV heater with pre heater and tankless gas unit if needed. I am not familiar with the marathon if it is heat pump type. Remember many inverters will produce about double their continuous rating for 5 to 20 seconds which may aid in starting the heat pump. Low frequency transformer units generally do this better than high frequency transformer or transformer less units. The sure=start decreases LRA by up to 70 %. You are smart to have a woodturning stove. In winter without grid sell you would have to have about double the PV panels and triple the batteries to be totally off grid even with efficient heat pump in cooler climates. You are often warming air 40 degrees or more in heating mode but cooling 20 degrees or more in summer so you need twice the energy to heat but only have about half the sun power available.
 

Ghcoupons

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To original poster. I have a 3 ton inverter heat pump that varies from30% to 130 % of 3 ton rating its a nordyne unit renamed for maytag taipan and Fridgidair among others mine is 21 or 22 seer and max draw is 11.9 amps and it ramps up slowly never going over this 11.9 amps. It also has dual fuel with gas backup. I also have a climate master tranquility geothermal open loop system that is 2 stage with a scroll compressor and soft start grundfus well pump. The 2 stage units typically ron at about 60% of rated tonnage or full rated tonnage and start with stage1 then later progress to stage 2 if needed. I have no trouble starting the inverter unit with a 5,000 watt inverter. I am currently looking at 13,000 watt inverter and using a sure-start soft starter which should reduce the LRA of 150 on my 5 ton unit to about 44 amps or less.

Other suggestions for saving power and loads are a heat pump type dryer that generally uses about 450 watts and not all even require a vent. Also a heat pump or direct PV water heater or preheater. I use a PV heater with pre heater and tankless gas unit if needed. I am not familiar with the marathon if it is heat pump type. Remember many inverters will produce about double their continuous rating for 5 to 20 seconds which may aid in starting the heat pump. Low frequency transformer units generally do this better than high frequency transformer or transformer less units. The sure=start decreases LRA by up to 70 %. You are smart to have a woodturning stove. In winter without grid sell you would have to have about double the PV panels and triple the batteries to be totally off grid even with efficient heat pump in cooler climates. You are often warming air 40 degrees or more in heating mode but cooling 20 degrees or more in summer so you need twice the energy to heat but only have about half the sun power available.
Something jumped out at me in your post that I’ve not looked into; Direct PV water heating. I did a quick search on YouTube and Engineer775 had a couple videos on it, and it really peaked my interest. I do need to see if my marathon can work with that or not. The marathons are made by Rheem and their lifetime warranty and low standby loss is what sold me in our last house. I went with them again in our current house we built. I know the heat pump style of water heaters are more efficient, but the purchase cost was the same, we have a tank of hot water if/when we lose power, and I can fix most things on a marathon myself for little cost. If a heat pump water heater breaks, I don’t have the skill set to repair them. Plus, their tanks don’t have a lifetime warranty Like the marathon does with a polybutene inner tank. Weather I’m correct in my thought process above is a mute point now as we already have the marathon installed. Lol.

I don’t know what details I need to look into to see if a Marathon would work with PV direct, but I surely would like to find out. In a grid down situation, having hot water and even well water would be at the top of my list. Thanks for your reply and for alerting me to this option.
 

Hedges

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A heat-pump water heater isn't likely to work PV-direct. An induction motor needs surge current to start. If it was inverter-drive (variable frequency drive) then it would soft start. But PV would always have to be >= 100% of load. To be PV direct, should vary motor speed to maintain MPPT of PV. That would be what Grundfos PV-direct deep well pumps do.

PV direct resistance heating works because as resistive load pulls down voltage, current draw is reduced. It finds some point on PV I/V curve to operate, but not maximum power point.

The problem with PV direct DC power of a water heater element is that the thermostat is designed for AC, will burn up on AC. Over-temperature cutout will have the same failure if triggered.

There is a company selling 48V 700W water heater elements. At least that's what's stamped on the unit. Vendor says 48VDC.
One of the forum members bought one and burned up the thermostat. When he opened the assembly, thermostat was stamped 230VAC.

Whether resistive or heat-pump, easiest thing to do is run it off an AC inverter, enabled when you have enough battery charge or PV generation.
 

TKB4

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Answer to both above . The whole benefit of direct pv is not to use battery storage or need larger inverter or more batteries and also avoid the energy loss in conversion. You do NOT have to use special elements you just need an element that meets the correct resistance to work with your panels. An Mppt controller helps use more of the panels energy especially if not in full sun but not absolutely necessary. David Poz has a table that will allow you to choose which element you need many of which are $20 or less elements available at your local supplier. You DO need to avoid use of the original AC thermostat to control the Direct PV power.
You can replace one element with direct PV in most water heaters (usually the lower one) or both if you wish and you can preheat water in a second water heater that then provides the preheated water to the primary water heater that may or may not need to heat it further. The unit Engineer 775 AKA Scott Hunter AKA Practical Preppers sells is the one designed and ? produced by Techtalk whose you tube channel is no longer available but his website Techtalk,com is. There are questions about its long term durability raised on this forum also. I highly doubt that marathon would warranty the tank if they knew the element was changed to non standard etc but you wouldn't have to and not sure how they would ever know.
 

Ampster

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The whole benefit of direct pv is not to use battery storage or need larger inverter or more batteries and also avoid the energy loss in conversion.
If one takes a system approach, the difference in efficiency by using a heat pump far offsets the inefficiency of directly heating water with a resistance element. I agree that on an incremental basis just adding the correct element may be a cost effective way to store some energy in lieu of buying a larger inverter and/or more batteries.
 

TKB4

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If one takes a system approach, the difference in efficiency by using a heat pump far offsets the inefficiency of directly heating water with a resistance element. I agree that on an incremental basis just adding the correct element may be a cost effective way to store some energy in lieu of buying a larger inverter and/or more batteries.
agreed but its also not just efficiency in the equation its installation simplicity in some cases portability or moveability etc. The ability to DIY installation or any other modifications required make any efficient system much more attractive though and is a value added to the property when done to professional standards.
 

Hedges

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The unit Engineer 775 AKA Scott Hunter AKA Practical Preppers sells is the one designed and ? produced by Techtalk whose you tube channel is no longer available but his website Techtalk,com is. There are questions about its long term durability raised on this forum also.

Have a link to that heating element?
On another thread here we had a tear-down of a water heater element + thermostat marketed for DC but turned out to be build of an element labeled for AC. And it failed.

If I did this, I would use the AC rated thermostat and over-temp switch for pilot duty to control a DC rated switch.
I hesitate to rely on solid state (transistors) to open-circuit as a safety device because I expect them to fail shorted. I've done enough electronics design to see that a number of times.
A suitably rated relay is one possibility. I have other tricks up my sleeve.
 

TKB4

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agreed but its also not just efficiency in the equation its installation simplicity in some cases portability or moveability etc. The ability to DIY installation or any other modifications required make any efficient system much more attractive though and is a value added to the property when done to professional standards.
Have a link to that heating element?
On another thread here we had a tear-down of a water heater element + thermostat marketed for DC but turned out to be build of an element labeled for AC. And it failed.

If I did this, I would use the AC rated thermostat and over-temp switch for pilot duty to control a DC rated switch.
I hesitate to rely on solid state (transistors) to open-circuit as a safety device because I expect them to fail shorted. I've done enough electronics design to see that a number of times.
A suitably rated relay is one possibility. I have other tricks up my sleeve.
There are several places that sell DC rated elements most of which are low wattage I will try to link the info to the table. There is also a video on how to disable the emergency recovery of heat pump water heater so it only uses the heat pump mode. Here is a link to his video with some of the table on it but he tells where you cab enter your panel data directly into the spread sheet that is on a site of his . I didn't watch it again to find out where this is, He talks and shows part of the table around 6 to 9 minutes into the video.

I hope this is helpful. He doesn't actually heat his hot water with this he uses liquid circulation panels to a heat exchanger for his to about a 200 gallon non pressurized rpm rubber tank in his crawlspace. Another you tuber to look at is devil destiny has some videos about direct PV heating .
 
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