Hey John, glad you have gone down this path, it has saved me a lot of money in running costs over the past 4 years. And you know, no guest has ever complained that it is not as warm, or as cool as they expected. I think they just accepted what they got as being the limitations of the system installation.
Now John that stopped the unnecessary wastage of a/c power while the guest was on the premises but, there is no need to stop there!
There is always going to be that guest that goes out for the afternoon and evening and just leaves the a/c running. Well John I have got that one beaten as well. We live in a marvelous age, and this is a gem!!
https://www.jaycar.com.au/240v-wireless-controller-switch-to-suit-home-automotion/p/LA5575
The guest cottage key is equipped with a remote sender, it's in that yellow pouch.......
and when the guest walks out through the front gate it automatically triggers a receiver which actives the Jaycar wireless controller and, after a 5 minute time-out period, deactivates the power supply to the a/c.
As soon as the guest walks back in through the gate the a/c is automatically re-energised and springs back into action.
The guest might think it's a pretty inefficient heating/cooling system when they enter but within 5 minutes it's up to speed and they forget all about it!
All my lighting is sensor touch lighting, the shower screen is automated up/down and I try to make the whole place as user friendly as possible John.......it all works seamlessly and it keeps me free from large power bills!
Cheers.........Rob
That's all good info John,
I appreciate your situation where you are just trying to give your guests a bit of additional comfort to that which your central system provides....and good on you John, you are a thoughtful host, the backbone of Airbnb!
My comments are directed more at 'stand alone' systems rather than 'whole house' supplementation.
Our situation in Australia is considerably different to yours. I understand in Charleston you are paying 14c pr Kw/hr, here in Australia we are paying double that amount with average cost of 30c pr Kw/hr which has pushed the bulk of us into installing our own rooftop solar. Now having rooftop solar is fine but, it doesn't solve our problem as a nation. Much of the year Australia gets by totally on solar and wind power alone which means governments have let grid power generation system deteriorate! But John, the infrastructure has to be maintained....the poles, the wires, the transformer network so, as more users convert to solar generation, supply revenue falls and the supply charge has to increase to maintain the network. We pay virtually nothing for any electricity we have to import between 10 am- 2 pm but, we pay an arm and a leg between 6.00 pm and 6 am.
Going green is a bit like a dog chasing its tail......you never actually make any positive headway!
With my two rooftop systems I can produce about 56 Kw/hr of electricity on a reasonably sunny day.........
and granted with my feed-in tariff that gives me a power credit through the summer months. Here was our balance with our supplier a month ago......
Winter months are a different story though! Now we will get monthly bills of around $140-$160. So it doesn't take long to eat that credit up.
The reason I bring this up John, before I put in my last 5 Kws of solar I was getting winter quarterly power bills of $1,800 + ....... and guests were responsible for 70% of that. At my age it is not worth me putting in battery storage. I see little point in paying off $8,000 worth of batteries that someone else will get the benefit of once age compels us to sell!
So that is why I have gone to considerable effort to stop power wastage. We don't go without or scrimp on power here.....we just don't waste it!
Where the Jaycar wireless controller could be useful in situations such as yours, it could be incorporated into the system ductwork via a control damper to your listing space. That way, when guests are not present the available output could be channeled into the main house!
But if I was only paying 14c pr Kw/hr I maybe would not have bothered going to such lengths although in this era of climate change every bit we can do to help makes us better global citizens!
All the best John.
Cheers.........Rob
A little bit of context to my unit. Before I renovated the back apartment it had 71/2 ceilings and didn't have any insulation. It really wasn't even usable space despite being connected to the central heat and air it was like having all the widows open year around.
I was gong to just add a kitchen area and live back there myself as I was working out of state and not here much. 
So in the middle of the revocation I decided to insulate the ceiling, which meant having to demo the old ceiling and build another. The advatge was being able to raise the ceiling to 10 feet.
Thats when everything changed.
I realized how nice it was and could rent it out. I was amazed how much rent cost. Then started googling Airbnb and was really surprised so many were in my area!
I added all new insulation, you can see some in the picture, all new windows on the entire house, and insulated the attic and crawl space.
The result was my elective and gas bill was cut in half. Even with the Airbnb my bill averages $140 a month, added an apartment that used to be like being outside.
So with it really well insulated there is a point of diminishing returns with how effeciant the ac/heat unit needs to be. I have it dialed in to the ideal size. So likely won't notice any real improvements over this.
Later I plan to add solar panels. I recall @Robin4 has them on his place.
The major cost is having the AC/Heat units replaced. There is another regulaton being passes that will add another 1K on the the cost of a new unit and also increase the cost of maintenance and repairs. Never mind that it doesn't matter how well insulated the house is.
My friends 600 square foot apartment cost over $500 per month for AC. it's the landlord, slum lord, that keeps crappy AC unit.
I didn't want anyone to think I didn't care about energy. I've already cut my power bills in half just by renovating and packing it with insulation.
If it was the old space with no insulation it would cost 3X as much to cool and heat.
For now I just don't want guest to break the mini split. It would cost 3k to replace.
Also not a one has turned it off when they go out. Sometimes they will turn it off if it's too hot or cold but no one turns it off coming and going.
But do what makes you happy! If it really cost a lot to heat and cool then my all means structure your house rules to conserve more! We all have to make some compromise and communicate.
For mine it's best to just leave it at one temp. It would cost more if guest turned it on and off. So I'm using the remote so guest can't break the equipment.
This remote I think will extend the life of the unit and will pay for itself probably in the first year.
Above all it makes me happy! I don't need to monitor the temps, or stress when guest turn AC down to 61, as they no longer can turn it below 69.
