Which system is more beneficial:Drain Back or Glycol

System

My name is smith, resident of Morrisville, North Carolina. I have no more Knowledge about Solar System. i want to install a solar water heating system for my home. but, when i was trying to install Solar Water Heating System, I just stuck at the point which type of system we have to install : Drain back or glycol type system. which system is more beneficial according to environment?

Solar Guppy

Re: Which system is more beneficial:Drain Back or Glycol

drainback is for areas that don't freeze ... your area would be glycol, meaning there is always fluid in the collector and pipes

Having answered that, Solar is no longer cost effective as the new generation of hot water tanks are heat-pump based. they cost on third the cost of a typical solar thermal system and use half the energy of resistive based hot water tanks, they also work regardless if its sunny or cloudy or dark out side.

I have installed and owned solar thermal, its not worth the hassle now that these new energy-star water heaters are available.

http://www.geappliances.com/heat-pump-hot-water-heater/

Dave Angelini

Re: Which system is more beneficial:Drain Back or Glycol

Looks like we disagree on drainback SG also. Drainback is the way to go for area's that freeze. It will never be as efficient as open loop but it is a simple way to avoid the hassles of ethylene glycol and the damage it can do over time.

Drainback had a bad reputation for the drain valves not working correctly but all that has changed in the last 10 years with mature design. You just walk by the tank and observe the level and you know that there is not water in the collectors. This can be automated and just a green light will tell you that all is well.

I do not spend any time with grid electronics and electric heatpump water heater heaters so I defer to those who do! For offgrid we use propane back-up to solar domestic hot water and radiant heating. It is essentially free energy (once payed for) that is extremely efficient! In many area's that support all year PV, the back-uip propane is not really needed.

It is an easy project for do-it-yourselfers if you have some time.

Solar Guppy

Re: Which system is more beneficial:Drain Back or Glycol

My experience with solar thermal is something always fails and if your relying on an automated control to prevent damage, it WILL get damaged at some point. Solar thermal is not free, for a system installed by a contractor your looking at ~4K, for less than half of that you can have the heat-pump hot water, which is a very efficient use of electricity. ( close to 8,000 btu's per kWh )

There is also the concern of running water lines above the ceiling and roof penatrations for the pipes on the collector. I had a collector fail, and came home to water running into the boot from the pipe in the roof and water into the ceiling of the garage, what a mess. Everything I have read and experiences suggests solar collectors are 100% sure over time they will fail.

I can see the differences of on/off grid, but even with offgrid, you have to power the circulation pump and pay for propane at night or cloudy days with you want to enjoy the modern convenience of hot water.

The post is just to show options and real world problems solar thermal has, there are real issues with it and between cost and reliability of these systems.

westbranch

Re: Which system is more beneficial:Drain Back or Glycol

SG, was there a particular part or was it a weld seam that failed? Poor material that rusted out? or ?

Eric

russ

Re: Which system is more beneficial:Drain Back or Glycol

İ have solar thermal and have not had any problems with it but İ agree with Solar Guppy 100%.

The dedicated water heating heat pumps give a COP of above 2 (2.0 to 2.5) and need to be located correctly. İt does no good to use warm air from you electric or gas furnace as feed for the water heater.

Please note these units are specifically designed to replace the hot water tank - nothing to do with a whole house unit. They are much more efficient as they typically go for lower water temperatures.

Over a 13 year period and considering electric rates of 10 cents the heat pump style winds hands down. By their calculations a solar thermal system would cost approximately 170% to buy and operate over the 10 years as compared to the heat pump type - Energy Star rated models include:

AirGenerate ATI1266
GE GEH50DNSR***
GE GEH50DXSR***
Rheem HP50RH
Rheem EcoSense HP50ES
Richmond HP50RM
Ruud HP50RU
Stiebel Eltron ACCELERA 300

ACEEE has a pdf file on line about this.

pbartko

Re: Which system is more beneficial:Drain Back or Glycol

I agree with Russ. Heat pump units can be very efficient and effective for southern climates. Florida is a good example where most water heaters are located in a hot garage. The heat pump will heat your water and cool your garage at the same time.

For northern climates, the heat pump will be removing heat from your home to heat your hot water. Many hot water heaters are located in conditioned spaces. That is my case here in Maryland. We have a heat pump as our main source of heat for the house. If I installed a hot water heat pump, during winter months, I'd be essentially running two heat pumps to heat my hot water, effectively reducing each system's performance.

Solar may be a better choice for northern climates in situations like this.

Pete B

sub3marathonman

Re: Which system is more beneficial:Drain Back or Glycol

I did a bit of checking. The Stiebel Eltron ACCELERA 300 lists a Coefficient of Performance vs. Temperature chart at http://www.stiebel-eltron-usa.com/accelera.html (download brochure), and if you're where it is hot, at 95°F you'll be getting a COP of 6, and even at 68°F the COP is 4. The downside, of course, is it costs about $3K.

Solar Guppy

Re: Which system is more beneficial:Drain Back or Glycol

There is no requirement that the heat-pump hot-water needs to be in conditioned space, as with AC heat-pumps, they will operate down ( and below freezing ) and still get better than a COP of 3.0

For northern climate, any space above freezing would work, typically a basement. The GE unit has a lower COP I believe because it has modes that use both the heat-pump and resistive elements in high demand times but can be programed for many modes, hence the hybird name. Technically there isn't any difference between a heat pump I have outside the home and what goes on top of the hot water tank and even moderate weather, its way above a COP of 4

As sub points out, for moderate climate, we can heat the hot water AND cool the garage, which also saves on the cooling load for the home keeping the garage temperatures down

This is on my list of wants, but I have so much PV I don't need to save electricity at the moment as I pretty much net out over the year now, once I get a EV, then, I'll probably get a heat pump HW tank.

Dave Angelini

Re: Which system is more beneficial:Drain Back or Glycol

Solar Guppy wrote: »

There is also the concern of running water lines above the ceiling and roof penatrations for the pipes on the collector. I had a collector fail, and came home to water running into the boot from the pipe in the roof and water into the ceiling of the garage, what a mess. Everything I have read and experiences suggests solar collectors are 100% sure over time they will fail.

I can see the differences of on/off grid, but even with offgrid, you have to power the circulation pump and pay for propane at night or cloudy days with you want to enjoy the modern convenience of hot water.

The post is just to show options and real world problems solar thermal has, there are real issues with it and between cost and reliability of these systems.

Just for anyone who is offgrid, you do not have to put collectors on the roof. In fact, you should not because you probably have the space and are in the position not to have penetrations in your roof.

Everything fails over time!

The El cid and the Taco, both commonly available hot water pumps use less than 20 watts, and run only when there is sunlight.

The system is designed to store the sun's energy and never uses propane at night if there was sun during the day. If sized right, it is just like PV only better in producing heat on cloudy days.

You do have to know what you are doing or hire someone who does!

russ

Re: Which system is more beneficial:Drain Back or Glycol

No problem with roof penetrations if done well - a leak with mine would just run off into the gutters - the location was designed with the solar thermal panels in mind.

Look at the Energy Star site for the COP values - that is where İ got the 2.0 to 2.5. The manufacturers would show the better rating they can manage so on an annual average basis they are probably correct. That is the main selling point.

The heat pump for a dhw system is different in the aspect that it is designed for higher water output temperatures. İ set my outdoor heat pump for 30 deg C on and 35 deg C off. That lets it operate most efficiently and it suits the 'in floor radiant' heat system as well as the fan coils. Every degree higher reduces the COP.

A dhw system operating at 50 deg C (120 deg F) would have a substantially lower COP.

Dave Angelini

Re: Which system is more beneficial:Drain Back or Glycol

russ wrote: »

No problem with roof penetrations if done well - a leak with mine would just run off into the gutters - the location was designed with the solar thermal panels in mind. Yes but you still have to go up there...

Look at the Energy Star site for the COP values - that is where İ got the 2.0 to 2.5. The manufacturers would show the better rating they can manage so on an annual average basis they are probably correct. That is the main selling point. I wish I could trust these guy's...Energy star should be getting better in a few months as they initiate a new "top ten" program

The heat pump for a dhw system is different in the aspect that it is designed for higher water output temperatures. İ set my outdoor heat pump for 30 deg C on and 35 deg C off. That lets it operate most efficiently and it suits the 'in floor radiant' heat system as well as the fan coils. Every degree higher reduces the COP. [For you guy's on the grid this is great. When you are on your own grid, water heating for domestic or radiant can not come from electricity at night. If it did, you would pay dearly to do this. Why do you say it is different? A water collector can easily produce 150F water in winter

A dhw system operating at 50 deg C (120 deg F) would have a substantially lower COP

I still like the COP on a couple collectors that just use the sun 90% of the year

LucMan

Re: Which system is more beneficial:Drain Back or Glycol

smith wrote: »

My name is smith, resident of Morrisville, North Carolina. I have no more Knowledge about Solar System. i want to install a solar water heating system for my home. but, when i was trying to install Solar Water Heating System, I just stuck at the point which type of system we have to install : Drain back or glycol type system. which system is more beneficial according to environment?

I recommend flat plate panels,& drainback system that work well in freezing climates.
Drain back is simpler and maintenance free, no antifreeze to replace every few years, less chance of stagnation during a power failure or pump malfunction. The pumps will use about 1KWH a day of power to heat 80 gallons of water from 55-130 degrees. If you change your anode rods on the water tank it will last 20 + years.
pumps last 15+ years. Of course your major fuel source is the sun which make it more environmentally beneficial.
Heat pump water heaters are also a good alternative, but have more parts to malfunction. expect a few service calls to repair relays, contactors, fan motors, and element replacement.
When the compressor malfunctions better to replace with a new water heater.

russ

Re: Which system is more beneficial:Drain Back or Glycol

Look at the system costs over time (13 years) as projected in the attachment to the last post. Solar thermal is 171% of the heat pump.

Service calls for the heat pump? Maybe so but should be little.

@Dave Sparks - Get to the roof - rather easy, İ just open a skylight and go on the roof - again the home was designed with that in mind

Trust Energy Star? Energy Star only points one in the right direction. Then it is time to do your own research. At least it weeds out a lot of the more flaky types.

A solar thermal collector can do what you want - if it reaches 65 deg C (150 deg F to people still using the English system) in the winter then you will have 3 times the panels needed in the summer and overheating problems. Unless you want to get on the roof and cover up some of the panels.

The COP on collectors is fine - the investment is excessive as the companies are holding up everyone at present. No way a system for a normal home (say 2 panels) should cost in the 4500 USD range. The investment far outweighs the COP no matter what kind of math one does.

Off grid the simple collector system makes sense - you adjust your life style to the system capacity. İ see no reason İ should do that when grid connected.

LucMan

Re: Which system is more beneficial:Drain Back or Glycol

Here is the latest Hi Brid system. This is the way home DHW and spaceheating-cooling is going.
Available soon in the US.
http://www.daikinac.com/residential/altherma.asp?sec=products&page=53

Solar Guppy

Re: Which system is more beneficial:Drain Back or Glycol

Don't see how it deals with condensation for southern climates and would cost way more then a typical forced air central AC / Heat pump system?

LucMan

Re: Which system is more beneficial:Drain Back or Glycol

Solar Guppy wrote: »

Don't see how it deals with condensation for southern climates and would cost way more then a typical forced air central AC / Heat pump system?

It is an all in one A/C- heat pump - DHW system, produces chilled water for A/C use in southern climates for dehumidification and cooling. The comfort level from radiant heating is well worth the additional cost.
I personally am uncomfortable with the constant air movement from hot air or heat pump systems, but that's my opinion.

Solar Guppy

Re: Which system is more beneficial:Drain Back or Glycol

You can't use the floor for cooling or you get condensation on the floor. The link shows each room needs a air exchanger unit. Forced air is required, its the only way to have the condensation removed that I'm aware of

LucMan

Re: Which system is more beneficial:Drain Back or Glycol

you are correct you need a chilled water fan coil for cooling,the same fan coil can also be used for heating if you want.
The system is designed for radiant floor heating because of the low water temps produced ( 115 degrees).
In September a high temp unit will be released with temperature capability of 180 degrees, this will be a cascade system ( 2 compressors). This system is designed for retrofit applications with radiators or baseboard.

russ

Re: Which system is more beneficial:Drain Back or Glycol

The problem with the house heat pumps that can also provide dhw is that you must run the entire system (say 5 kW) when making hot water for the tap. The addition of the dhw side is more or less of an 'oh, by the way'.

İn my situation, The heat pump is on part time during the winter and İ didn't turn it on for A/C at all last year. Be rather inefficient like that and not good for the compressor life - cycling on and off. As İ mentioned before mine is set on a 35 deg C (95 deg F) water temp for the infloor hydronic heating and that will work with the fan coils as well.

The newer style dhw heat pump, as in the pdf file LucMan attached is designed for year around use for dhw only. The higher output temp leads to the low (for a heat pump) COP.

For 80 deg C water (180 deg F) the COP would be nothing like we are accustomed to seeing - the lower the output temp the better.

Solar Guppy is right - you can not use a hydronic floor system for cooling. Some claim you can use it in walls but condensation is a real problem. İ have individual drains from the individual fan coils (ceiling mounted) to the plumbing system.

The hydronic 'in floor heating' is primary but if additional heat or more rapid heat is required the fan coils can be used. All cooling (except for natural type) is by the fan coils.

Dave Angelini

Re: Which system is more beneficial:Drain Back or Glycol

russ wrote: »

A solar thermal collector can do what you want - if it reaches 65 deg C (150 deg F to people still using the English system) in the winter then you will have 3 times the panels needed in the summer and overheating problems. Unless you want to get on the roof and cover up some of the panels.

This does not happen with a drainback system by the way.

newenergy

Re: Which system is more beneficial:Drain Back or Glycol

Top tier energy pricing for electricity for Southern California Edison is almost 40 cents per kwh.

Also Solar hot water gets federal tax credit and sometimes utility rebates as well.

Just saying the cost analysis(es) itt might not be correct for everyone.

--

Also, no one has electric water heaters in my part of the country. I haven't really looked into the economics but everyone here goes with natural gas.

Dave Angelini

Re: Which system is more beneficial:Drain Back or Glycol

newenergy wrote: »

Top tier energy pricing for electricity for Southern California Edison is almost 40 cents per kwh.

Also Solar hot water gets federal tax credit and sometimes utility rebates as well.

Just saying the cost analysis(es) itt might not be correct for everyone.

--

Also, no one has electric water heaters in my part of the country. I haven't really looked into the economics but everyone here goes with natural gas.

And wait there is more, if you act now, it is one of the easiest home brew projects there is. Without any credits you can start with a simple open loop system, buy everything from Home Depot except the pump and a 15 watt panel and have free hot water, at leaset 6 months of the year, no matter where you live for under 1K$.
The more advanced drainback and radiant projects will be easier once you have the basics. THX. BB for my edit fix. I missed learning those office skills on the boat...

BB.

Re: Which system is more beneficial:Drain Back or Glycol

Dave,

You are very welcome!

On the solar hot water--I have a natural gas hot water tank (standard 60 gallon).

One of the reasons I have not installed solar hot water was I was always looking at having to install ~80 gallons worth of storage (bit of a pain to find a place for it in my garage/home (there is a handy place outside if I wanted to add a lean-to on the outside).

Are you looking at just heating the water in the existing natural gas fired heater?

-Bill

Dave Angelini

Re: Which system is more beneficial:Drain Back or Glycol

BB. wrote: »

Dave,

You are very welcome!

On the solar hot water--I have a natural gas hot water tank (standard 60 gallon).

One of the reasons I have not installed solar hot water was I was always looking at having to install ~80 gallons worth of storage (bit of a pain to find a place for it in my garage/home (there is a handy place outside if I wanted to add a lean-to on the outside).

Are you looking at just heating the water in the existing natural gas fired heater?

-Bill

Yes! It is so easy! even a 40 gallon tank, an El Cid pump, a pv panel, a timer, a thermal switch, and a 50' coil 1/2" copper tubing, 2 tee's, 4 valves + some time and basic material. My point is not to knock the new technology, many do not have the time or it may not be worth the hassel.

LucMan

Re: Which system is more beneficial:Drain Back or Glycol

BB. wrote: »

On the solar hot water--I have a natural gas hot water tank (standard 60 gallon).

One of the reasons I have not installed solar hot water was I was always looking at having to install ~80 gallons worth of storage (bit of a pain to find a place for it in my garage/home (there is a handy place outside if I wanted to add a lean-to on the outside).

Are you looking at just heating the water in the existing natural gas fired heater?

-Bill

You can retrofit your existing 60 gal. tank with about 40-50 sq. ft of panels
A 10 gallon drain back tank doesn't take much room, you can make a shelf for it next to the existing tank.
Could give you enough hot water to turn off your gas from May to October, depending on how much hot water you use.
I have 78 sq. ft. of collector on a south east roof & 80 gal. preheat tank before my 30 gal. indirect and have used 130 gallons less of fuel oil per year.

russ

Re: Which system is more beneficial:Drain Back or Glycol

İ like the diagram of the drain back system - the ones İ knew about before always had the tank at the top which are super ugly.

My system (İzmir, Turkey - insolation similar to Los Angles) has 3 Schuco panels - electric backup to the tank is now turned off and will reamin that way until November sometime. İn March it was on and off depending on the cloud situation - used 51.5 kW for the month (element only). Naturally the recirc pump is always on when the panel is warm enough.

The recirc pump consumes between 0.4 and 0.8 kWh daily depending on the pump speed setting selected.