Replies

1. Expert Member
   Dana Dorsett | Aug 14, 2014 02:37pm | #1

   For new construction in 5a climate it's usually possible to design-out most of the cooling load.

   Coupled with high efficiency AC or heat pumps (like ductless mini-splits), the amount of money you would spend on thermal ice cooling systems would be better spent on grid-tied photovoltaic systems. Thermal ice systems make financial sense in some commercial building applications where the utilities are assessing "demand charges" during peak grid-load hours to recover the operating costs of low capacity-factor peaking generators, which can sometimes be more than 2/3 of the bill, but residential rates don't have those features.

   PV delivers a large fraction of it's rated output during the tradtional peak grid-load hours, and are effectively a peaking generator on YOUR side of the meter. Sometimes it's cost effective in commercial applications to have both ice systems AND PV, but I can't imagine a residential application where that would make any sense at all:

   http://www.greentechmedia.com/articles/read/how-sun-power-and-ice-energy-can-play-together

   For a residential application you can offset more grid-peak hours simply by orienting the PV toward the SW or W rather than due south, where it delivers more kwh overall, but slightly less power during the late afternoon/early evening grid-peak hours.

2. 
   Nathan_Kipnis_FAIA | Aug 14, 2014 03:53pm | #2

   Illinois, where the project is located, does have varying power rates for residential including real time pricing where nighttime power is significantly lower, even near zero cost at certain times. That is the time when the power is coming from the nuclear fleet (uggh) and the large number of wind turbines. Community Choice Power Aggregation has allowed communities that want it to obtain 100% renewable energy, or that can be set up individually, which would be done in this case.

   The concept would be to use the very low or zero carbon power at night to freeze the ice (store the cooling), and the PV panels to make it through the day for most of the rest of the loads. This is in addition to all of the other standard efficiency measures being done to the house - reduced size as much as possible, tight shell, proper orientation and shading, efficient appliances and lights, etc.

3. Expert Member
   Dana Dorsett | Aug 15, 2014 11:16am | #3

   Time-of-use rates for residential users does not compare to demand charges assessed on commercial rates anywhere that I'm aware of, but electricity markets are evolving pretty rapidly- I certainly can't speak with authority about every local market.

   I have to apologize- the wording in my previous answer regarding demand charges miss the mark by quite a bit- was being pretty sloppy. It's not related to the peak GRID load, but rather, the peak loading at the RATEPAYERS site.

   Demand charges look at the magnitude of the peak energy use (typically on 10 or 15 minute intervals) at a facility, and are designed to cover the utility's infrastructure costs of having to support that magnitude of load. Unlike time of use rates, demand charges do NOT reflect the wholesale cost of the electricity- the per-kwh electricity use cost is a separate line item (and can be either fixed, time of use, or continuously variable- depending on what rate structures are offered.) Demand charges can be pretty steep- if your peak 15 minute load is 500kw but your average load is 10kw, the infrastructure costs for supporting your peak load is pretty substantial. If you can use ice-storage to run fewer/smaller compressors, or use battery storage on your side of the meter to run manage huge but short-term loads to get your peaks down to say 50kw or less it will often pencil-out very favorably. It's common for demand charges to be more than half the bill in commercial applications.

   Variable residential rates tend to only reflect the variable wholesale cost of electricity, and even that is usually buffered a bit from the absolute peak wholesale costs of electricity, and the grid-use charges are usually fixed on a per-kwh basis, even when the energy charges are varying by time of use.

   In CA residential PV owners are now allowed to have battery storage on their side of the meter, which probably has greater flexibility & greater economic value than a thermal-ice storage system. I'm not sure if or when that option would be coming to IL.

   But the short answer to your original question is, SFAIK nobody is currently marketing ice systems small enough to be applicable in for residential applications.

   Utilizing the thermal mass of the house and smart thermostats to pre-cool the house to avoid peak time-of-use rates is pretty cost effective & easy, and in new construction designing the house for higher than average thermal mass can help cooling peaks considerably.

4. 
   Nathan_Kipnis_FAIA | Aug 15, 2014 11:43am | #4

   Thanks Dana. I hope someone can bring a cost effective ice storage system to the residential market. Unfortunately, I think with the rising temperatures forecast in the future, cooling systems will need to become even more efficient and work efficiently with the grid. In the meantime, we will consider exactly what you are suggesting.