I just sent this by PM, but in case anyone else cares:
I do this for boats. It's a different audience, but similar challenges. You have a couple of 'bursty' loads - the water heater and the compressor in the heat pump. Everything else is pretty mild. You really have two options, size for peak and run at lower capacity, or size for average and manage your loads accordingly.
In the boat world generators get used a lot more. Typically daily if people are at anchor. Generators don't like to be run at 50% capacity (or less), there are issues with wear when the engine is running and there can be issues with the generation side too with losing residual magnetism and other problems. So in the boat world, people will generally size lower (this also gets you efficiency and space advantages) and then they mange their loads by using the genset when cooking and charging batteries. They also adjust their loads according to the available power and will turn off heat pumps while cooking or take other steps to keep the load in the 75-90% range of the generator capacity.
In the backup world (not emergency), this is less important. You will probably have more test/maintenance run time on your generator than actual use. And since your actual use to power your house is likely to be small an infrequent it won't matter so much if it is unloaded a lot of the time. You also don't have space considerations like a boat, and efficiency isn't a huge deal either. So all that considered I'd say you are probably better off with the 20KW solution where you don't have to manage loads as long as the cost difference isn't that big.
If the cost is big, you are also fine stepping down to a 17 or even 13KW unit as long as you remember to only do one or two things at a time. 13KW will give you 54 Amps, so even when heating water you are fine with other things as long as the heat pump compressor doesn't try to spin up.
I looked up a 90F + day from June of this year and peak usage was just over 5kw. Is that the figure I should use (plus 25%)?
Well yes and no. That's your average load. Your problem is your average is skewed by your efficiency. There is big gap between hot water on and hot water off, so while average is informative you probably need a bit more than 25% reserve for sizing. When your heat pump starts it probably pulls 70 amps by itself, but only for a few milliseconds (look up the LRA - Locked Rotor Amps on your compressor). So if you are cooking and the fridge is spun up and the water heater is on, the compressor won't start. This isn't the end of the world, it probably just won't start, worst case is it will trip a breaker. This is the 'managing your loads' bit above. Your peak usage is really your hot water heat, and a set of appliances, I'm guessing wildly, but I'd put your peak at around 50-55A. I think you would be fine with any of the systems, but it will take more management on your part for each level you step down.
I just sent this by PM, but in case anyone else cares:
I do this for boats. It's a different audience, but similar challenges. You have a couple of 'bursty' loads - the water heater and the compressor in the heat pump. Everything else is pretty mild. You really have two options, size for peak and run at lower capacity, or size for average and manage your loads accordingly.
In the boat world generators get used a lot more. Typically daily if people are at anchor. Generators don't like to be run at 50% capacity (or less), there are issues with wear when the engine is running and there can be issues with the generation side too with losing residual magnetism and other problems. So in the boat world, people will generally size lower (this also gets you efficiency and space advantages) and then they mange their loads by using the genset when cooking and charging batteries. They also adjust their loads according to the available power and will turn off heat pumps while cooking or take other steps to keep the load in the 75-90% range of the generator capacity.
In the backup world (not emergency), this is less important. You will probably have more test/maintenance run time on your generator than actual use. And since your actual use to power your house is likely to be small an infrequent it won't matter so much if it is unloaded a lot of the time. You also don't have space considerations like a boat, and efficiency isn't a huge deal either. So all that considered I'd say you are probably better off with the 20KW solution where you don't have to manage loads as long as the cost difference isn't that big.
If the cost is big, you are also fine stepping down to a 17 or even 13KW unit as long as you remember to only do one or two things at a time. 13KW will give you 54 Amps, so even when heating water you are fine with other things as long as the heat pump compressor doesn't try to spin up.
I looked up a 90F + day from June of this year and peak usage was just over 5kw. Is that the figure I should use (plus 25%)?
most sites that sell or install generators have power calcs
i think kohler has a good one
the way you roll? whole enchilada will be about 20 kw
maybe consider natural gas too
many here have them set up to kick on in a split second
Been looking at our power usage on the utility's website; I'm thinking the 13kw unit will be sufficient. Yes, it will be natural gas-fueled. We'll probably set it up with a 1-2 minute delay before starting; we have a lot of random power blips that last only seconds.
think of it like a great scotch
you want the bigger bottle
if you have a major outage, a neighbor or friend may want to pull his camper up in your driveway
for what i've seen when you have electricity and others don't, you'll have an opportunity to be a life saver
make a lot of friends, sort of like miss twiggley's tree
most sites that sell or install generators have power calcs
i think kohler has a good one
the way you roll? whole enchilada will be about 20 kw
maybe consider natural gas too
many here have them set up to kick on in a split second
Been looking at our power usage on the utility's website; I'm thinking the 13kw unit will be sufficient. Yes, it will be natural gas-fueled. We'll probably set it up with a 1-2 minute delay before starting; we have a lot of random power blips that last only seconds.
I just sent this by PM, but in case anyone else cares:
I do this for boats. It's a different audience, but similar challenges. You have a couple of 'bursty' loads - the water heater and the compressor in the heat pump. Everything else is pretty mild. You really have two options, size for peak and run at lower capacity, or size for average and manage your loads accordingly.
In the boat world generators get used a lot more. Typically daily if people are at anchor. Generators don't like to be run at 50% capacity (or less), there are issues with wear when the engine is running and there can be issues with the generation side too with losing residual magnetism and other problems. So in the boat world, people will generally size lower (this also gets you efficiency and space advantages) and then they mange their loads by using the genset when cooking and charging batteries. They also adjust their loads according to the available power and will turn off heat pumps while cooking or take other steps to keep the load in the 75-90% range of the generator capacity.
In the backup world (not emergency), this is less important. You will probably have more test/maintenance run time on your generator than actual use. And since your actual use to power your house is likely to be small an infrequent it won't matter so much if it is unloaded a lot of the time. You also don't have space considerations like a boat, and efficiency isn't a huge deal either. So all that considered I'd say you are probably better off with the 20KW solution where you don't have to manage loads as long as the cost difference isn't that big.
If the cost is big, you are also fine stepping down to a 17 or even 13KW unit as long as you remember to only do one or two things at a time. 13KW will give you 54 Amps, so even when heating water you are fine with other things as long as the heat pump compressor doesn't try to spin up.
most sites that sell or install generators have power calcs
i think kohler has a good one
the way you roll? whole enchilada will be about 20 kw
maybe consider natural gas too
many here have them set up to kick on in a split second
Been looking at our power usage on the utility's website; I'm thinking the 13kw unit will be sufficient. Yes, it will be natural gas-fueled. We'll probably set it up with a 1-2 minute delay before starting; we have a lot of random power blips that last only seconds.
Forgot about your on demand electric water heater. That will kick up the loads a bit. Id still call that peak and add 25 % or so ( you onlybuse that when you are heating water). Remember that you want to be able to average 50 - 75% load capacity on yiur genset, or you will introduce other problems.
what wre your available increments on generator capacities?
are you doing split phase 240? 20 kw is around 80 amps at 240v. That's a lot of juice, but with hot tub and other loads you might get there on occasion. Still feels high for an efficient home. Lighting is normally a big load and you went all led right?
take your last powee bill and divive kwh bu the hours in the month. That's your average load. Peak is porbably 1.75x or so
Probably. We had a tankless electric water heater installed last year; it pulls 40 amps all by itself. While our attic is insulated to R60, our windows are still original equipment - something I hope to rectify incrementally. All lights are LED, yes.
Forgot about your on demand electric water heater. That will kick up the loads a bit. Id still call that peak and add 25 % or so ( you onlybuse that when you are heating water). Remember that you want to be able to average 50 - 75% load capacity on yiur genset, or you will introduce other problems.
what wre your available increments on generator capacities?
are you doing split phase 240? 20 kw is around 80 amps at 240v. That's a lot of juice, but with hot tub and other loads you might get there on occasion. Still feels high for an efficient home. Lighting is normally a big load and you went all led right?
take your last powee bill and divive kwh bu the hours in the month. That's your average load. Peak is porbably 1.75x or so
Probably. We had a tankless electric water heater installed last year; it pulls 40 amps all by itself. While our attic is insulated to R60, our windows are still original equipment - something I hope to rectify incrementally. All lights are LED, yes.
I redid ourbold house with high efficiency stuff, and i ran the whole place off an 8kw generator with lots of overhead.
consider a transfer panel with a subset of circuits - do you really need the guestbroom whennpower is out? Lights, tv, cold beer, hot water- no judgement on whatborder you put them in.
I was hoping you were around...
I want to be able to run the house as normal - the whole house.
are you doing split phase 240? 20 kw is around 80 amps at 240v. That's a lot of juice, but with hot tub and other loads you might get there on occasion. Still feels high for an efficient home. Lighting is normally a big load and you went all led right?
take your last powee bill and divive kwh bu the hours in the month. That's your average load. Peak is porbably 1.75x or so
I redid ourbold house with high efficiency stuff, and i ran the whole place off an 8kw generator with lots of overhead.
consider a transfer panel with a subset of circuits - do you really need the guestbroom whennpower is out? Lights, tv, cold beer, hot water- no judgement on whatborder you put them in.
I was hoping you were around...
I want to be able to run the house as normal - the whole house.
NOT DIY... We will be having installed a standby generator next year. Sick to death of Baghdad Electric's outages.
Our home is approximately 1,000 sf and our appliances modern and efficient. In addition to the generator, we'll be replacing our package unit furnace/ac with a full-electric heat pump. From what I gather, a 20kw unit will be more than adequate; looking at a Cummins because they're very quiet.
Anyone have any experience with such things?
I redid ourbold house with high efficiency stuff, and i ran the whole place off an 8kw generator with lots of overhead.
consider a transfer panel with a subset of circuits - do you really need the guestbroom whennpower is out? Lights, tv, cold beer, hot water- no judgement on whatborder you put them in.
NOT DIY... We will be having installed a standby generator next year. Sick to death of Baghdad Electric's outages.
Our home is approximately 1,000 sf and our appliances modern and efficient. In addition to the generator, we'll be replacing our package unit furnace/ac with a full-electric heat pump. From what I gather, a 20kw unit will be more than adequate; looking at a Cummins because they're very quiet.
Seems our local Lowe's doesn't carry diamond-tipped bits, only diamond-ground carbide bits. But, one of those got the job done - a lot faster than I anticipated. Job went off without a hitch; the most difficult part was removing the old fixture.
What sort of bit does one use to drill a hole in ceramic tile?
I have a set of diamond 'hole saws' I use to drill through ceramics. They look like tiny hole saws, without the drill in the middle. They are tricky to use by hand, but it's possible. Especially if you don't need precision. google 'diamond hole saw', Amazon has a set for under $10.
Carbide tip masonry bit. FIRST make a nick with a sharp awl or something to scratch it, then I use a very small bit to start. Put some masking tape or duct tape on it first, to help keep the bit from walking. The bit should also have a sharp point to help it stay put. You have to get through the glazing carefully. Once you get the small bit thru the harder outside, you can go to the full size bit. If you sprang for a new super hard diamond tip masonry bit, you might not need to do the small/large bit thing, but I go with what got me here. DO NOT apply much pressure. I keep the bit speed pretty fast but not maxRPM, and pressure very very light. It will go, eventually, but it takes patience.
I'm thinking I may be able to place the hole in the grout between a couple of tiles... or is that not a good idea?
Will the tile be on the floor on on a wall? I assume you're thinking of a small hole. If it's for something like a towel rack a penetration in a grout seam could eventually loosen or crack the grout because of the repeated strain of pulling and pushing towels on it, though even that may not happen right away. If it's for something like a water supply line it may not matter as much. Either way, a lot of (flexible) caulk or silicone around the perimeter is usually good.
Carbide tip masonry bit. FIRST make a nick with a sharp awl or something to scratch it, then I use a very small bit to start. Put some masking tape or duct tape on it first, to help keep the bit from walking. The bit should also have a sharp point to help it stay put. You have to get through the glazing carefully. Once you get the small bit thru the harder outside, you can go to the full size bit. If you sprang for a new super hard diamond tip masonry bit, you might not need to do the small/large bit thing, but I go with what got me here. DO NOT apply much pressure. I keep the bit speed pretty fast but not maxRPM, and pressure very very light. It will go, eventually, but it takes patience.
I'm thinking I may be able to place the hole in the grout between a couple of tiles... or is that not a good idea?
