Buffer or Indirect Tank 4 DHW

nooboo

Planning for Domestic only Hot Water today!



In your minds eye, keeping it simple here, picture a 3.3kw in 15kw out liquid to water ground source heat pump (GSHP) with the domestic on it's own priority zone.

Just focusing on Domestic...(very high deltaT, on the order of 80 degrees F) How to complete the picture given the GSHP limitations, no cooling loads, no desuperheater bs.



I am seeing an buffer tank, prioritized, then run the water in buffer tank to a heat exchanger then into a Electric water heater to get the temps up to 5 girl hour shower temp range. I like an indirect water heater from the GSHP, then into the electric heater, but the temp rise will be inadequate from the coil in an indirect. So, a Buffer Tank of some size is how it is done?

SWEI

how much headroom

From the space heating loads?  A big tank might just do the trick, and keep the delta-T down to where the heat pump can work well.



Any other fuel sources?  How much sunshine there?

nooboo

Fuel Sources

Fuels sources run the gamut. Thinking about one example: a neighbor built a multi-fuel hot water heater big enough to cook a horse in, he burnt waste oil, phone books, stumps, It was a one owner Appliance. He was away and had someone else run it and that guy burnt most of his Blue Board off it from over firing. Well, when my own indestructible days are over, I hope to have an easy way to heat hot water. I live in a nice place, but we just need to capture a few more BTU's. My running of the numbers show that electricity is currently a push, at 15 cents a KW and $4.40 gallon diesel. Diesel is my current method; works well with a 90% eff Quietside Boiler. A SS heat coil in the wood stove to warm some of that cold well water before it hits the Quietside. The new GSHP is the direction; incorporating solar is a fine idea, especially from April to September, but sunshine is variable, this year is so far snowy and sunny; Flat plate solar probably, not so much concentrating solar ; I have a hot air beer can system in progress...



What do you mean headroom.?

SWEI

headroom

How much of the time does the GSHP have to run 24x7 to satisfy the heating load?  The remaining portion of that time (if there is any) represents headroom which can be used for DHW heating.



If you have a reliable supply of wood on site, biomass gasification could save you a pile of money and give you some security against fuel price uncertainty.

nooboo

KW

This Heat Pump is going to have to work Very Hard to keep up with our loads, so not a lot of headroom, eh? I could give values in BTUs or KW, here: KW, as that is the heat pump's values: House is 6KW/hour averaged over our coldest months, with stoking of the wood stove fairly hard as a supplement. We burnt 9 cords of spruce last year. This house is big, well insulated, lots of triple pane windows. $7000/yr in Energy costs, 40k pounds of CO2/yr (per the energy calculations), my actual was less.



GSHP is 14KW in theory (3.3kw in) I can feel this is close and the house may will be cold some of the time.

SWEI

heat loss calc

Do you have a heat loss calc at design temp?



It's starting to sound like you could use a bulk heat source during the colder months, then let the GSHP handle the shoulder seasons.  I'll ask again about wood, because if you have that on site, a gasifying cordwood boiler plus storage (or something like a Garn) would be a great fit.

nooboo

Gross BTU

Gross Loss per hour is 52,000.



The current Boiler is Quietside QXM8 80kbtu which does a fine job for both domestic and radiant, not sure if the unit is made still.



That Garn looks a bit like the home made unit my neighbor built. Would you think the 1500 is the way to go? We certainly could find lots of uses for Zoned heating, like for shop, high tunnel, garden bed warming. Biomass availability is not a problem; cutting lets say 40 cords of wood may be. Lets say btu gross loss per hour *25*365=455,520,000 divided by my cordwood btu value (spruce) 18,000,000 = 25 cords * efficiency factor of well, what is a garn? Can I say 50%, if so, that is 50 Cords. I am the the Willow, AK Chainsaw speed cutting Champion for 2009 and 2010; I Can do it!



I did think about a big mass gassifier and a small mass gassifier. The Garn has a big jacketed heat source; is that right? I can look it up. Just looking for ideas. I see you wrote OR a Garn; I get it. Maybe a gassifier with my big indirect tank. I have bought a big tank...It is 2500 gallons and I plan to super insulate it and maybe swim in it...The problem I have with the wood is not that I am not willing to slave to the thing, not afraid of hard work, I don't like the dust of the wood inside the house and I am a **** about going outside every few hours when it is 20 below (f). I see the gassifiers need to be indoors. Could do that too. Maybe replace the woodstove with a new Garn Sofa. I'll see what Lisa says about it.



Still need to figure out the DHW. The water for domestic would preheat in the indirect tank, then if needed, get boosted to user hot water temps, maybe it would require a mixing valve to not scald the folks.

nooboo

Design Loss

Design Loss is 97,000, Gross Loss is 52,000

SWEI

wood gasification

Will hit 80-85% efficiency - that's the point.  If you already have storage, check out the AHS (a domestic gasifier with a long track record) http://www.alternateheatingsystems.com/WoodGasification.aspx  There are quite a few European manufacturers of similar designs, though neither shipping costs nor exchange rates are favorable at the moment.



The idea is to load the boiler once per day (usually less) and consume the entire fuel load, storing all of the BTUs.  I'd store at 180F, then mix down with a motorized mixing valve and ORC.  You can pipe the mixed output in series with your GSHP if you coordinate the setpoints, and the GSHP will not kick in until the tank runs out of BTUs.

SWEI

wood-fired heat sources

http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_10_us.pdf is an excellent resource.

nooboo

Talking

So far, so good...Just talking about say, the Wood Gun, given a design loss of 100,000BTU's what is an appropriately sized unit? ... Given: Low value wood Black Spruce in small diameters, but dry, which you realize has a lot less heat value per cord than many other type cord woods.

SWEI

it's really about the storage

If you store at 180F and your system design temp is 120F (just guessing here) your 2,500 gallon tank will hold about 7.5 million BTUs.  AHS can help you figure out the BTU value of a load for each of their boilers based on species, dryness, and size.  Then you decide how often you want to load the boiler and how much you want to spend...