Best way to minimize energy usage w/ mini split system

Hi everyone

Just got my Freidrich mini-split system installed yesterday. Installer recommended leaving the system on all the time, at 78 degrees when not at home.

It seems as though the units never shut off at this setting (expanded cape, very hot upstairs, which is why we bought the units).

I'm wondering if I should follow his advice, or just turn the system on two-three hours before we need them in unoccupied (really hot upstairs rooms) rooms? He said the system takes a while to cool it down, thats why it should be left on.

can anyone corroborate (or dispute?) this recommendation? I'm a little worried about the electric bill, between this and the basement dehumidifier that also never shuts off

 

What is the temperature upstairs with the unit running?

 

I leave my house at 77f when I leave for the day. On a day like today where it's 90f outside.... it may not even recover from 77 to 73 or 74 when I get home and lower it.

It may take a little experimenting on your part to see how fast it can cool based on outside temperatures.

 

If the space hadn't been conditioned for a while, it's going to run for a while, removing humidity from furniture and carpeting before you even realize the cooling effect. I'd keep it at 78 for a few days and see if you see a difference then.

 

thanks for all the feedback! I actually had an issue with the new system and was focused on that (only one head was blowing cold air after the first day!?!... Installer came back in, checked the charge--I think thats what its called--which was fine. He said sometimes the valves get stuck due to sitting at warehouse, etc and sometimes just powering off/on will free them up. Sure enough, today--the day he came by, everything was working before he got here)

Temp upstairs seems to get to 88F+ without ACs on. I'm tempted to leave windows open and ceiling fans on upstairs until early afternoon and then put the system on around 2pm @ 77 degrees

 

I guess I'm wondering if leaving the system on all the time at 77 degrees is more energy efficient than turning them off 7am and on 2pm (or later?)

 

As has been mentioned, moisture removal is one of the primary duties of any air conditioner and opening windows in NJ may defeat much of the gains.

It sounds to me like the AC installer ignored the number one advice for energy efficiency, improve the house first. Throwing a mini-split at a poorly insulated and air sealed home is not going to give the best results.

You have probably done some work insulating, but the statement "expanded cape, very hot upstairs" says more is needed.

Bud

 

interesting. I was wondering if having insulation contractor blow in cellulose insulation would actually save any money, given that there is no attic. Maybe that whole house energy audit isnt such a bad idea..

 

when I say 'very hot upstairs', I mean without any AC. With the two units running up there, its pretty comfortable. Easily get it down to 72 degrees--they just run (without necessarily using condenser) pretty much all the time. Thats why I raised the question initially-- to see if others run their mini-splits all the time, or only when home and the heat makes it uncomfortable...

 

The whole house energy audit (if done completely) can tell you how much energy is being lost through each wall, ceiling, or floor in every room. Rarely done, except by geeks like myself, and not often necessary, but it does lead to the bad spots where most attention should be focused.

Your electric bill will be your first indicator as to how efficiently this system is working with your house. As you mentioned, "running" doesn't mean the compressor is running.

Bud

 

well, had audit Monday. Waiting on results. I can tell they're going to recommend some serious insulation work upstairs (no surprise) and will build a compelling case toward replacing the boiler (its about 25 years old).

That one will be a tough pill to swallow. My contractor friend said to keep that in place as long as it will last (this model apparently is known for longevity). Replacing a functional, yet not as efficient boiler seems like significant expenditure with a long payback horizon.

We'll see what the report says...

 

Definitely share the report with us.

Unfortunately, a heating plant is a large investment.

 

Won't your Mini-split be able to pick up some or most of your heating load?

Bud

 

mini split could off set heating... But I am not sure how the math works yet.

What I mean is that a 70-75% efficient boiler using (relatively?) cheap natural gas for whole house (1800sq ft) heating overnight vs an electric powered heatpump heating two rooms (700 sq ft)

 

As requested, here is what the Energy Audit company proposes

1) Replace current boiler (Weil-McLein, approx 20 years old, 75% effiecency)
2) Replace current water heater (AO Smith GCV 40 200, built 2008)

For 1 & 2, they are recommending a Navien NCB-240 -- 93% AFUE

Additionally, they are giving me 2 options for insulation

Option A: basically insulate 'flat' ceiling areas and knee walls with cellulose
Option B: same, but with sprayfoam (more expensive)

Price diff is $1100 (1+2+A or 1+2+B)

They are claiming I will see a 36% savings on heating/cooling/hotwater usage... Without a years worth of bills, he could only estimate this at approx $600 annually.

Post incentives, I would be looking at 9-10k for this job... That's a lot of years for payback, right?

 

Where's the audit?? If that is all you got, ask for your money back, that was just them charging you to prepare their own estimate for the job.

Blower door: CFM50
Window area and heat loss.
Wall area and heat loss
Ceiling/slope area and heat loss
Foundation heat loss

And there is a lot more that constitutes a real energy audit. From that, yes they can offer their proposal for work, but you should be able to take those results to other contractors for bids as well.

That data is yours and you paid for it.

Bud

 

just asked the company... Thanks for this! My daughter was running around and it was hard to pay attention so I didnt think to ask yesterday...

 

So the auditor replied.

He says the state (NJ) forces him to use software that it uses standard values that are not very accurate. He has offered to give me a copy of the report, but warns that the report software hasnt been updated in 10 years, and the pct savings module hasnt been updated in over 4 years.

Whats starting to annoy me is that I decided to do this audit primarily to make a case to justify the expenditure on insulating my upstairs. I am not getting any concrete savings info out of this. Just a 36% number that isnt grounded to my utility bills as I hadnt lived in the house a full year.

 

It sounds like you got the classic run-a-round that gives energy auditing a bad name. Antique software excuse to cover his backside as the numbers he promised are just standard guesses.

Here is a link to a comprehensive energy audit data collection form:
http://blog.sls-construction.com/wp-...field-form.pdf

And there can be a lot more beyond the standard data, the things we look for outside of the typical. From this data they sort out what the software needs and generate various estimates.

In many cases they don't use the home owners actual energy data, although I ALWAYS try to be sure we are in the ball park. They determine the before (current) use based upon what they find. Then they adjust those numbers for the proposed improvements. The difference in energy use between the two is the projected savings.

If a home owner has already been very cautious with their thermostat and other energy uses, then they will now see the projected savings.

Show them the form above and ask them to fill in what they collected. Than ask for your money back because I'm assuming they will have very little to fit into that form.

If they don't like that form I can find others very similar, all used by real energy auditors.

Bud

 

thanks for this!

Will ask him to fill this out...

 

Insulation will not do much for reducing your cooling cost. Most of that will be radiant heat that most insulation will not stop

 

thnx airman...

Sounds like most of savings will be on heat...?