In a recent thread ("Benefit of Staying in First Stage"), joe.ami wrote: "It would be interesting for one of our friends with a WEL to monitor unit with 5 degree set-back recovery."

Having a WEL unit and being pretty versatile at using it (I'm at http://welserver.com/WEL0043 ), I thought I'd offer some comments on this.  I started a new thread here so as to not dilute from the discussion in the other thread on the benefits (or lack therof) of forcing one's unit to stay in 1st stage always.

I've thought for some time on how to devise an experiment to quantitatively determine the answer to a key question: is there benefit to using a set-back/recovery tstat scheme versus keeping one's residence at a constant temperature.

With a fossil fuel furnace, I believe the answer is clearly 'yes,' there is benefit to using a set-back/recovery tstat scheme.  With duct register output temp on the order of 130° (F), it doesn't take as long to heat up a residence, assuming the furnace is properly sized and in good working order.

But for a heat pump, with register output temps that are usually between 90 and 100°, it's not clear to me at all if it saves money or costs more to use set-back/recovery.

In my case, we maintain our living areas at 68° and our sleeping areas at 65° during the day, all areas at 65° at night, and warm up the bedrooms to 68° for a few hours in the morning.

Thus, the question I keep wrestling with is if this set-back/recovery scheme is really saving money versus a strategy of simply running the home at 68° on a 24x7 basis.

As Dwayne, Joe and others have noted, outside temperature is a key influencer.  If the weather pattern were to stay consistent from day to day, then it would be easy to experiment.

But in fact, weather changes quite a bit.  And a number of days are required to run the experiment to adequately account for structure/contents heat absorption/loss.

A good compromise is thus to measure cost as a function of Heating Degree Days.  Since cost can vary as a function of local pricing, a better measure of cost would be KWH usage.

So I believe setting up an index, like KWH / HDD, would provide the data to do the experiment.  Here are some suggestions to Dwayne and others who have WEL units on how to set up an experiment.

First, set up a power monitor just for the GSHP unit(s).  In my case, I have this at  http://welserver.com/cgi-bin/plot/WEL0043/DailyKWHConsumption.gif .  The dark blue line shows accumulated GSHP KWH usage for each day.  For the past 20 days it has ranged from 10 to 50 KWH per day.

Next, set up a HDD monitor.  In my case I have this at http://welserver.com/cgi-bin/plot/WEL0043/MonthlyDegreeDays.gif .  The red line shows accumulated HDD for the month. 

For the purposes of doing an experiment, this chart would need to be done on a daily, not monthly basis.  Also, configuring a WEL to track HDD can be a little tricky, due to the need to understand how accumulation fundamentally works, but, it can be done in fact with a high degree of precision.  An outside temp sensor is of course needed.

Lastly, take each 24 hour's KWH usage accumulation and divide it by the same day's HDD accumulation to arrive at the day's KWH/HDD.

For example, for yesterday, my GSHP units consumed 16.2 KWH, and HDD = 12.0 (avg temp was 53° here in Dallas yesterday).  Thus, the KWH/HDD index for yesterday was 1.4.  I.e., I 'burned' 1.4 KWH for every degree the day's average temp was below 65°.

For the day before, as another example: KWH = 23.2, HDD = 16.9.  Thus, index = 1.4.  Here we see consistency from one day to the next: this day was colder (lower avg temp at 48°) and thus more KWH were 'burned, but the index, at 1.4, was the same.

To substantially eliminate the effects of structure/contents heat loss/absorption, I'd run the experiment on a 1 week basis.  I.e., run the home at a constant 68° (or whatever is desired) for a week, then run the home at the desired set-back/recovery scheme for another week.

My guess is the day-to-day 'index' values during each week will be similar, like illustrated above.  What I don't know is if the index value will improve or degrade when implementing the set/back recovery scheme.  But that's the key question to be addressed with the experiment.

Note that my suggestion here requires on-the-side, manual analysis to figure up each day's 'index.'  I've thought for a while on how to set up the WEL to automatically compute these daily 'index' values and chart them, but, I haven't yet figured out how to do it.  Fortunately the WEL also provides a minute-by-minute data log of anything you'd want to record.  So the data is in the log.

Hope this helps, especially to Dwayne who said he was going to do an experiment to try to quantitatively figue out if indeed set-back/recovery schemes save money or not.

Best regards,

Bill

cant wait for the results

Bill,

Do you know that 65 is the appropriate basis for zero heat demand in your home? Just because the weather service likes 65, doesn't mean it is the right temp for you to use in these calculations. I suggest using as a HDD basis whatever average outdoor temp results in zero heat needed for your house. I seem to recall you have large kwh use outside of HVAC, which suggests you might have significant internal loads, lowering your zero heat balance temperature.

I believe you are attempting a 'slope' calculation aka y=mx+b. You want 'm', but I think you'll need 'b', the zero intercept.

Just a thought...

Curt

Thanks Bill and again Dewayne for your experiments. It is interesting to me that we don't already have a source for this information. You guys maybe cutting edge.
I look forward to the results, and many more.
J

Bill,

thanks for bringing this back to the front.

I tried to do this, but the weather pattern didn't hold. I realized then that I needed to do an HDD analysis, but put it off mostly because I didn't know how to set it up on the WEL.

I will gladly add my data if you can help me set up the HDD on the WEL.

Dwayne, the weather pattern here in Dallas is so unpredictable that I can't think of a way around using HDD.

So here you go.  Here's how to track HDD (and CDD) using a WEL, using my device names for example.  It is assumed that 65 degrees is the DD basis (Scale and Offset will change for DD if otherwise).

I've included below Scale, Offset, and Accumulation designations - each are fundamental to the calculations:

A01 = (outside temp sensor in centrigrade) * 1.8 + 32

DD = (A01 + Zero) * 0.041667 - (minus sign) 2.708330 with 'B' accumulation

DDC = DD } Zero ( '}' is used in place of '>' )

CDD = DD * DDC with 'B' accumulation

HDD = DD - CDD with 'B' accumulation

To summarize above, 5 'device slots' are needed; one for the sensor and 4 'Expression' slots.

CDD for today / this month -> CDD_D, CDD_M

HDD for today / this month -> HDD_D, CDD_M

My chart that I mentioned in my initial posting here is Red=HDD_M and Blue=CDD_M.

For this experiment, be sure to include in your log HDD_D, and retrieve the midnight values for each day's HDD.

Holler if you have questions.

Best regards,

Bill

Will the recovery time include a Aux heater source? My guess is using Aux heat will have a big impact on your figures. It would be interesting to see recovery cost with and without the Aux heater enabled. I too am looking forward to your results, to finally settle the matter of weather setbacks are worth the effort. After the last electric bill, I too started playing with setbacks, but I'm also setting back an ASHP which will make determining what GSHP savings difficult.
 

Curt, I initially used 65° (F) because that's what the U.S. weather services use, and I wanted to check my calculations to verify accuracy.

Later, now that I think about the appropriateness of 65° as the basis for zero heat demand for my home, it seems reasonable.  My home 'burns through' about 15 KWH per day of misc usage - lights, computing equipment, cooking, entertainment, etc.  I know that 15 KWH per day can be computed to a BTU/hr equivalent.  My guess is I'm pumping enough heat into my house such that a 68° tstat setting at the same time it's 65° outside will result in zero heat demand.  Qualitatively, it seems reasonable.

I agree the experiment can be perfected by finding the zero intercept.  In fact, if I were to leave my tstats set without change for a long time period, I believe all I'd have to do to determine the zero intercept is plot a bunch of index values, and then extrapolate the slope.

You could also argue the experiment can be perfected by taking into account wind speed, noting that houses have varying permeability.

But, I think what's being asked is if a good amount of set-back/recovery is cost effective, and not just a 1° set-back/recovery.  As such, although the experiment is not perfect, I think it can answer the question just with looking at HDD, and using an arbitrary basis for zero heat demand, such as 65°.

Also, you may ask why I don't just go ahead and do the experiment myself since I'm already set up to gather the data.  The answer is one of my 2 GSHP units is broken, and as such we're messing with the tstats quite a bit to maintain reasonable heating in the home.  It's not a serious situation since I don't have a weather pattern like many are experiencing currently up North, and since I have 2 units.  But, it does prevent me from doing the analysis with consistency.

I look forward to Dewayne getting HDD set up on his WEL.  I'm confident he can do it because it's no harder than doing COP, which he's already done.  And he already has a WattNode dedicated just to his GSHP unit.  So as long as he can maintain tstat settings that aren't arbitrarily changed for an experiment period, he should be in great position to answer the question (and then be able to well advise his customers, based with good solid fact.)

Best regards,

Bill

What is going on with your broken heat pump?

10-4 on the HDD

Sorry you have a unit down - better now than July, I suppose.

I'm hopeful to keep this thread focused on the benefits (or lack thereof) of using a set-back/recovery strategy tstat strategy when using heat pumps.  Thus, I'll start a new thread on my problem.  Look for a posting later today from me, with an image.  I'll additionally be graciously soliciting some advice on things to watch out and/or ask for when the repair is made next week.

Got that HDD computing yet, Dwayne, on your WEL?  The absolutely critical WEL Expression is the DD described above.  The associated Scale and Offset numbers are important, as they allow you to take advantage of the WEL's minute-by-minute accumulation ability.  The DD Expression essentially records the incremental amount of degree days for a minute time period in a 24 hour day, using a 65° basis.  Each of these incremental additions added up gives you degree-days for the day, as represented in DD_D.  The remaining three WEL Expressions are simply to split out HDD and CDD from DD.   Holler if you have questions.

Best regards,

Bill

Update!!!! I have messed this up some how so don't look at the data yet 


The charts won't make sense until tomorrow.




OK !!! thanks to Bill's excellent tutoring,  I have my WEL set up to accumulate:

KWH per day

HDD per _Day

KWH _per _HDD

or here

KWH per HDD



We will see how well this works.

Dewayne, I looked at your charts (at the bottom of http://welserver.com/WEL0114 ) and the format / structure looks good.  I understand your data for today is inaccurate - my guess is you're waiting for the WEL daily accumulators to reset at midnight for GSHP KWH and HDD.

I believe you'll struggle a little bit with the last WEL chart, KWH per HDD.  My guess is it will end up quite 'noisy.'  At the beginning of each day, when there's little HDD accumulated, you'll have a tiny number in the denominator of the division calculation.  In my case this causes large spikes in the data. 

Fortunately, it's just the end-of-day at midnight number that is of importance - a full day's worth of KWH divided a full day's HDD.  So don't forget to put into your logging the appropriate variables.

Don't forget that during an experiment period, you can't touch the tstats.  They need to be running the same set-back/recovery program exactly the same way every day for the experiment period.  Same for the experiment period where the tstats are set to a 7x24 constant setting - you can't let a family member temporarily make it warmer!  If you have kids, you may need a 'do not touch' sign for the tstat during an experiment period!

While I don't have opportunity at the moment to run a controlled experiment, I can still set up similar WEL charts to give you opportunity to compare to.  Take a look at the bottom of http://welserver.com/WEL0043 .  In my case, I only had 2 spare charts available, not three.  So I had to combine GSHP KWH and HDD on the same chart.  I expect my Index chart following to be quite 'noisy' - I'll be surprised if it's very usable.

Nice job getting this set up in your WEL unit.  Being able to compute HDD daily using a WEL takes advantage of some of the WEL's advanced accumulation features.

Best regards,

Bill

OK... After a 30 minute phone call to Bill last night,  I have my WEL calculating   KWH per heating degree per day.

You can see the chart here.

The line bounces around during the day as the KWH and HDD accumulate at different rates.  The value at the end of the day is the one we are interested in.  I will run my tstat with a set back for 5 days and then no set back for 5 days.  It will be interesting to see the results.

Our weather looks interesting for the next few days.

The results for the first day are in:

.644 KWh per Heating Degree Day.

The results for the are in:

First Day  =.644 KWh per Heating Degree Day.

Second Day = .752   KWh per Heating Degree Day.

I don't have a WEL system (wish I did) but attached is my daily data for my geothermal system electrical use.  I gathered this info from submeters that I had installed. 

As you may see from the chart, I tend to use between 1 and 1.5 KWH/HDD, this includes my electric aux heat use. 

I live in Upstate NY in an old farmhouse that is ~1950 sq ft.  I have a 3 ton WaterFurnace 038 (2 zone 2 stage + aux as 3rd stage) and a closed 450 ft vertical loop.

Dewayne, I've been watching your WEL charts with interest, looking forward to seeing the results of your tstat setback-recovery experiment ( http://welserver.com/WEL0114 ).

While the experiment is just in its beginning stages, I'd like to ask some questions on some things I'm already noticing.

I notice that for a day that has about an 8° F low, your GSHP only ran twice during the 24 hour period.  Once for a number of hours, starting early morning, to recover from the 5° night time setback.  And then one other time during late afternoon to maintain your ambient temperature.  That's it - 2 run-time cycles on a day with an average outside temp of 18°.

How do you accomplish this?  Excellent structure insulation and excellent air infiltration prevention are my two guesses.  And if so, I'm impressed.

I note further that during the day, as the outside temp is rising from about 18 to 25°, your interior ambient temperature correspondingly rises, and without your GSHP running.  Thus I'm guessing you must have some ability to take advantage of winter solar gain.

And lastly, I note how gradual your interrior ambient temp rolloff is - obviously why you don't have to run your GSHP for very many cycles during each day.

I am impressed!  Looks like as an excellent HVAC contractor, you "walk the talk," which I'm sure is an unbeatable sales strategy.

Best regards,

Bill
WEL0043

It's good to have some data regarding set-back. While I think much more is required it appears preliminary reports are positive to the tune of more than >10% (sorry I can't do the downloads).
I have some thoughts/questions not at all intended to be combative but for context purposes.
1) is the amount of loop you have typical of all your installs or did you throw in extra for your job (we use significantly less in MI and are holding our own in record cold)? Do you think ground loop size has impact on set-back recovery?
2) Did you originally suggest very mild temps (45*) in your area? Do you suppose that has an impact on savings? In lower temps with smaller loops could there be a point of diminishing returns?
I think you have done us a favor in providing some data on the age old question. Can we automatically extrapolate it into any field size?
We've recently suggested frost should never be on loop lines, yet it occured on one of our late installs when the night temps dropped to a (unofficial) -17*. Yet geo still performed. Would we suggest set back/recovery in those conditions and would we still be suprised with some frosting?
Is best service to customer adding cost to over design ground loops or keep cost at a minimum (given relatively low cost of a few hours of aux.)?
Again I ask as food for thought not criticism of anyone's design.
Our thanks again, Dewayne, for taking the time/trouble to perform this experiment.
Joe