Any suggestions on small circ pump?

[dogwood]

I am planning to put a twenty plate flate plate heat exchanger next to my 30 gallon Domestic Hot Water Tank. I need to find a small circ pump to pump the DHW from the bottom of the tank up through the flat plate hx and back into the top of the tank. Its a very short run with one inch pipe. Laing makes some small circ pumps but they are pretty pricey for what they are. Any suggestions for a more reasonably priced alternative. I am definitely going with the flat plate instead of a sidearm or other alternative. Thanks

Mike

 

[Nofossil]

I am planning to put a twenty plate flate plate heat exchanger next to my 30 gallon Domestic Hot Water Tank. I need to find a small circ pump to pump the DHW from the bottom of the tank up through the flat plate hx and back into the top of the tank. Its a very short run with one inch pipe. Laing makes some small circ pumps but they are pretty pricey for what they are. Any suggestions for a more reasonably priced alternative. I am definitely going with the flat plate instead of a sidearm or other alternative. Thanks

Mike

I ended up with a Laing for that application myself. I don't have the model number, but I got it off of Amazon for around $160. It's a nice units with a stainless cavity and ceramic impeller, if I remember right. The cheaper circs use cast iron and may not be what you want for potable water with loads of dissolved oxygen.

 

[in hot water]

the switch is on to stainless steel circs for DHW use. They tend to be a bit cheaper but the bigger reason is the California no-lead standard. To comply with that, which will probably go nationwide requires a special,expensive, harder to machine brass alloy.

I see Taco and Grundfos have cast or forged stainless volutes on most of their DHW circs now..

There will probably be a glut of bronze DHW circs on the market, cheap, when that standard goes into effect.

Depending on the pressure drop at the gpm you plan on flowing, you may need something like a Grundfos 15-18 or 15-42 to flow through that HX. The HX should have a spec for sizing the pumps.

hr

 

[dogwood]

I'm looking at only a 2.8 gpm flow on the DHW side of the flat plat hx and a 0.4 pressure drop for the Bell and Gossett BP400-20 model. The Bell and Gossett specs I am looking at are from a link on the PexSupply site. The spec sheet lists an appropriate Bell and Gossett pump, model NBF-9U, but it seems to be the pump on the boiler supply side not the DHW side. I'll look at the Grundfos pump curves to see if they are workable for such a small flow. I am not sure how pressure drop relates or converts to head either to be able to read the pump curve. Any suggestions there?. Are there any major differences between 20 plate heat exchangers of the same size that would warrant paying more or less? Some do seem to withstand greater pressure which is not needed. Anything else anyone know of?

Mike

 

[pybyr]

I'm looking at only a 2.8 gpm flow on the DHW side of the flat plat hx and a 0.4 pressure drop for the Bell and Gossett BP400-20 model. The Bell and Gossett specs I am looking at are from a link on the PexSupply site. The spec sheet list an appropriate Bell and Gossett pump, model NBF-9U, but it seems to be the pump on the boiler supply side not the DHW side. I'll look at the Grundfos pump curves to see if they are workable for such a small flow. I am not sure how pressure drop relates or converts to head either to be able to read the pump curve to tell the truth. Any suggestions there?. Are there any major differences between 20 plate heat exchangers of the same size that would warrant paying more or less? Some do seem to withstand greater pressure which is not needed. Anything else anyone know of?

Mike

The good quality flat plate exchangers have a "wavy" pattern embossed into all the internal plates (though it's not visible from the outside) in order to create turbulence in the water moving through- improves heat transfer and slows/ diminishes build-up of crud on the plates. I tend to wonder whether some of the no-name/low price plate exchangers may skimp on some things like that (which you really can't detect/ confirm unless you tear the unit open) in order to meet the far lower cost that they're selling some of them at, compared to the better makes.

 

[dogwood]

The Bell & Gosset ones PexSupply sells do seem to have a pattern on the inner plates. Thanks for the tip Trevor. And thank you too Nofossil and HR. What is the relationship between pressure drop and head loss? Is there a formula to convert pressure drop to head loss? Are they different concepts or are they the same thing differently named? I'm not finding a clear answer in the Siegenthaler book and want to make sure I size the circs on either side of the flat plate correctly by looking at pump curves, which list head loss not pressure drop. The flat plate specs only have pressure drop listed. It's another hydronics mystery.

Mike

 

[in hot water]

20 plate 5X12"? That's plenty of HX to heat 30 gallons of water in a timely fashion. HXers get sized by the amount of energy you are trying to move through them. Larger HX either dimension-wise or plate count, gives you more HX surface area.

On the "A" side the boiler side you need to know how many BTUs and the temperature in and out. Same on the "B" side DHw side. The manufacturers charts should give you the info, typically a B&G;rep will size the HX exactly to your need. Some manufacturers have design software on their website to size heat exchangers, or the local B&G;rep could help you size the right one. Really no need to grossly oversize.

Pressure drop, or the resistance to flow is expressed in feet of head. Pump curves read in feet of head also. So once you have the spec on the HX, look for a pump that moves the 3 gpm, or whatever, at the pressure drop the spec sheet shows. Typically a small circ is all you need on the DHW side. I think the "B" in the B&G;number indicates bronze volute.

hr

 

[dogwood]

The Bell and Gossett 20 plate flat plate hx I am looking at is only a 3"x8" rated at 125,000 btu's and is listed as a low pressure BPX brazed heat exchanger. My DHW tank is actually 40 gallons. Don't know why I remembered it as 30 gallons. Does that hx sound more appropriately sized for that sized tank. For 125,000 btu's the flow on the boiler side is listed as 5.2 gpm at a pressure drop of 1.5 ft of head. On the DHW side it callls for 2.8 gpm and has a pressure drop of .4 ft. of head. The chart shows you can lower or raise the amount of btu's anywhere from 75,000-150,000 btus by raising or lowering the gpms on the DHW side by increments of one gpm and simultaneously raising the bolier side gpms in .5 gpm increments.

My goal has been to reheat the 40 gallon tank in a similar timespan to what the propane fired burner does now, so no-one (my wife) notices any difference in DHW production when the propane is finally turned off. Some figures Solarguy provided ("40 gallons @ 90 degree rise = 29,988 btu’s per hr".) in a previous post lead me to believe the 125,000 btu's will enable us to reheat that 40 gallon tank in roughly fifteen minutes at 125,000 btu, which sounds reasonably fast. Appreciate your input. Have I finally figured this flat plate thing out or is there more figuring to do, other than getting the correctly sized circs.? Appreciate your input.

By the way, I'm mailing in my check to BioHeatUSA for a Solo Innova 50 tomorrow morning, already wrote it out. Can't wait.

Mike

 

[deerefanatic]

The Cheapy ebay exchanger I had had the "wavy" pattern on it too... And they are waaaayyyy cheaper than any name-brand you'll buy.. Mine was good to 435psi too.

 

[dogwood]

Matt, have you been pleased with the performance of your flat plate hx. What type of application are you using it for? I am a little concerned about acquring a "bargain" flat plate now. You wouldn't think there could be that much difference, but who knows. I'm going for the wavy lines though.

Mike

 

[in hot water]

your sizing sounds fine, go with it.

I think the bargain HXers work just as well. Really all they do in China is copy the design and build it much cheaper.

In some cases, however they use less grades, or questionable grades of materials. Sheetrock, paint, tires, etc etc. are classic examples of where costs are cut.

That being said, many of the major manufacturers have plants in China that build to strict US standards. B&G;has cast pump volutes there for years. Viessmann builds solar components there, the list goes on.

I think you "roll the dice" when you buy stuff for prices that are hard to believe. But I'm tempted to do it from time to time, for my own use. I'd have a hard time selling bargain basement product to my customer that I have to warranty for years.

hr

 

[dogwood]

Thanks for the confirmation HR. I think I will go with the Bell and Gossett flat plate hx rather than take a chance on a less expensive Chinese knockoff. I probably saved fifty dollars or so on a bargain Chinese bench vise I still have. It has been aggravating me for a decade or so since purchase, due to a binding turnscrew. I'll let that experience guide me. Have a good one. Thanks again.

Mike

 

[dirttracker]

Mike,

I have a 20 plate ~5x12 (it seems to be made to metric dimensions) for my DHW. It's a Sepescol brand (I thnk I have the speeling right), made in Poland I beleive. I don't know how it compares to the chinese stuff, but this has suited my needs for the last 6 years. I don't know what the price was, it came as part of a "kit" when I bought my OWB. The OWB is gone, but I still use the HX to heat domestic water directly. I have the plate hx with a tempering valve connected in parallel with a tankless LP water heater to supply DHW. I use the tankless LP at time during the summer months when I am not around to fire up the Tarm. I have no problems heating water to a comfortable temperature with hot side supply temperatures down to 130 F. When I had the OWB, the plate hx was connected in series to the inlet of my 40 gallon LP water heater, when I installed my Tarm the old water heater became my expansion tank. I did not use a circulator pump keep the water in the tank at temperature and had no problems with having a steady supply of hot DHW even if the water in the tank had cooled down a bit. I turned off the LP burner in the water heater during the winter so there was no "recharging" of the tank. It seems with this arrangment the heated water coming in the water heater tank would rise to the outlet and provide hot water even with cooler water in the tank. I offer this as a potential alternative to installing the HX with a pump (like a sidearm). I don't know if this will work for your situation, but if it does you could save the cost of a pump.

Eric

 

[dogwood]

Eric,

Sounds like a clever arrangement. Do you have an idea what the turn-around time is to reheat your tank if you use up your available DHW? I was particularly interested you could get usable hot water when your supply temp is down to 130 degrees. The specs for flat plates I've been seeing usually assume a boiler supply temp of 180 degrees. So I was going with what I thought was a bigger size, 20 plate hx, that can be run at higher gpms, if need be, to ensure it would do the job at lower supply temps between boiler firings. How do you like your Tarm by the way? I'm awaiting delivery on one.

Mike

 

[dirttracker]

Mike,

In the origonal configuration, when I had the OWB with the plate hx inline with the water heater inlet, I had hot DHW as long as the I had hot water from the stove. There was no need to allow the water heater tank to reheat, it had a supply of hot water going into the tank from the plate HX whenever there was hot water in use. Keep in mind, the OWB ran a water temperature between 150 and 175, so this was the hot side supply to the HX. If there was no hot water demand for a long time (12 hours +), hot water coming out of the tap initally was a little cooler than normal as there was some reduction in temperature due to mixing of the hot and cooler water in the water heater tank. However, I was always able to take a shower at my usual temperature, I just had to use a higher proportion of hot water until the water heater tank was fully up to temperature.

With my existing setup the DHW I get with a 130 F hot side temperature is just hot enough for me to shower with comfortably. I beleve this works if there is enough difference in flow rate between the hot and cold fluid. Based on my estimates I should have 5-6 gpm on the hot side of the HX and ~.5 gpm of DHW flow. I have not measured DHW supply temperature in this condition, but it's in the 100 F range. I'm sure I could not supply more than 1 DHW load at a time under these conditions, but it's not very often that I need to run more than 1 DHW load anyway. My system usually only operates under these conditions in the summer when I am using storage to heat DHW.

I really like my Tarm Solo 40. I ran it for ~2/3 of last heating season an until about a month ago for DHW. It uses a lot less wood than my OWB and smells much better

Eric