Finally -- Bus Heater Install!

[wsmurdoch]

[QUOTE=Juho;3141721]Yes, there will be heat losses in all the phases. One should however note that part of those heat losses will leak into the cabin.[
/QUOTE]

I'm not talking about heat losses from the system. I'm talking about temperature drops as the heat is transferred from the engine coolant, to the storage water, to the heater discharge air, and to the heated space. In order for heat to flow from one object to another, one must be cooler than the other. For usual systems designed for economy, the temperature drops of 10F (5C) are not unusual for liquid-liquid heat transfer and 20F (10C) for liquid-gas heat transfer. So, the storage water must be cooler than the engine coolant, the heater exhaust air must be cooler than the storage water, and the space to be heated will be cooler than the heater exhaust air.

The amount of heat that can be stored in water is the difference in temperature times the mass of the water. That difference has an upper limit set by the engine temperature and a lower temperature set by the desired minimum heated space temperature. In both cases the temperature drops mentioned above must be applied. Good (expensive) design can minimize the temperature drops. but they can not be eliminated.

I'm not saying that the idea can not be done. I'm saying that the sums need to be realistically worked out.

Bill

[belizesailor]

Originally Posted by Dockhead

I would love to have water ballast. 500 liters is like 6 or 7 guys on the rail.


I think in a new build it should not be that hard to accomodate such tanks, but insulating them would be a trick.

Ha, now just needs to be movable! Movable, heat sink/ballast. Make it a potable water tank too and now you have several uses!
[emoji6]

[Dockhead]

Originally Posted by belizesailor

Ha, now just needs to be movable! Movable, heat sink/ballast. Make it a potable water tank too and now you have several uses!
[emoji6]

Naturally not moveable. You have one on either side.


When you are keen to store heat, you could fill BOTH of them.

[Dockhead]

[QUOTE=wsmurdoch;3141790]

Originally Posted by Juho

Yes, there will be heat losses in all the phases. One should however note that part of those heat losses will leak into the cabin.[
/QUOTE]

I'm not talking about heat losses from the system. I'm talking about temperature drops as the heat is transferred from the engine coolant, to the storage water, to the heater discharge air, and to the heated space. In order for heat to flow from one object to another, one must be cooler than the other. For usual systems designed for economy, the temperature drops of 10F (5C) are not unusual for liquid-liquid heat transfer and 20F (10C) for liquid-gas heat transfer. So, the storage water must be cooler than the engine coolant, the heater exhaust air must be cooler than the storage water, and the space to be heated will be cooler than the heater exhaust air.

The amount of heat that can be stored in water is the difference in temperature times the mass of the water. That difference has an upper limit set by the engine temperature and a lower temperature set by the desired minimum heated space temperature. In both cases the temperature drops mentioned above must be applied. Good (expensive) design can minimize the temperature drops. but they can not be eliminated.

I'm not saying that the idea can not be done. I'm saying that the sums need to be realistically worked out.

Bill

My coolant temp is 80C and my calorifier gets to within 4 or 5 degrees of that after a certain amount of time.


So maybe not 50 degrees of Delta T but surely 40 or so. That's still 22kWh out of a 500 liter tank; 44 out of two of them. That's quite a bit of heat; a testimony to the high specific heat of water.

[a64pilot]

A not insignificant issue with trying to heat a large mass of water with the heater circuit is I’m pretty sure it bypasses the thermostat, and if you draw enough heat from it, may keep the engine from getting up to operating temp, or taking an excessive time to get there.
You could modulate flow with a valve though if that becomes an issue, cause you can block off flow from that circuit, many engines don’t have it connected, but have plugs installed.

[Dockhead]

Originally Posted by a64pilot

A not insignificant issue with trying to heat a large mass of water with the heater circuit is I’m pretty sure it bypasses the thermostat, and if you draw enough heat from it, may keep the engine from getting up to operating temp, or taking an excessive time to get there.
You could modulate flow with a valve though if that becomes an issue, cause you can block off flow from that circuit, many engines don’t have it connected, but have plugs installed.

I guess you could put a thermostat in THAT circuit, too, couldn't you. A couple of degrees less than the main thermostat.

[Juho]

Originally Posted by Dockhead

This is a pet peeve of mine. Our previous boat had a lot of exposed uncored fiberglass hull inside, and it was condensation city in cold weather.


This one is vastly better -- there is no exposed hull at all, the hull is fully cored, and there is insulation between the hull and the interior panels.


But the single-glazed windows and hatches are a problem. If you were new-building a boat for high latitudes you would definitely want double glazing of some kind or another.


As to heat recover ventilation -- it would be great, but I'm not sure how you would do it. A micro heat exchanger in each dorade? Doesn't seem feasible to me. Cold air whips through my dorade vents (6x big ones) in the winter but I've always regarded that as the price of having a well-ventilated and so fresh smelling boat.

I might put more even money on good insulation than on the heating systems. Such passive systems follow the agreed principle of keeping things simple. Ventilation with heat exchange is not as simple as plain physical insulation, but necessary if one is serious with being comfortable in cold and hot climates.

At least in Finland new windows in houses are nowadays at least triple glazed. No reason to have anything worse in boats. Well, except that strength against pressure of falling water comes first. If we are looking for simple and cheap solutions, it would be easy to add another layer of (double) glass below a regular hatch.

Heat recovery ventilation requires some new thinking. The time of the old approach of multiple hatches and Dorade boxes is over. From heat economy point of view that approach is very wasteful.

Basically one should have one big heat exchanger that takes its input from one (large) or multiple dorade boxes, and distributes that air to all required places in the boat. For windless days and nights, also a fan is needed, since good ventilation is essential also in well isolated boats. All return air will flow trough the same heat exchanger (that's why having only one heat exchanger could be the easiest solution). For nice warm summer days one could have the option to open various hatches and the companionway (in the traditional "cabriolet style").

[Juho]

[QUOTE=wsmurdoch;3141790]

Originally Posted by Juho

Yes, there will be heat losses in all the phases. One should however note that part of those heat losses will leak into the cabin.[
/QUOTE]

I'm not talking about heat losses from the system. I'm talking about temperature drops as the heat is transferred from the engine coolant, to the storage water, to the heater discharge air, and to the heated space. In order for heat to flow from one object to another, one must be cooler than the other. For usual systems designed for economy, the temperature drops of 10F (5C) are not unusual for liquid-liquid heat transfer and 20F (10C) for liquid-gas heat transfer. So, the storage water must be cooler than the engine coolant, the heater exhaust air must be cooler than the storage water, and the space to be heated will be cooler than the heater exhaust air.

The amount of heat that can be stored in water is the difference in temperature times the mass of the water. That difference has an upper limit set by the engine temperature and a lower temperature set by the desired minimum heated space temperature. In both cases the temperature drops mentioned above must be applied. Good (expensive) design can minimize the temperature drops. but they can not be eliminated.

I'm not saying that the idea can not be done. I'm saying that the sums need to be realistically worked out.

Bill

Another approach to estimating the heat requirements is to see the boat as a (hopefully well insulated) box that will get 500 l of extra hot water inside.

In this approach it doesn't matter much how the heat will find its way to the persons in the boat. The simplest approach is to have no active heat transfer systems at all, but to rely on having few (passive, non-insulated) hot containers in few key places in the boat.

One could for example have 100 l hot water under each of the five beds. The heat content of 500 l of hot water could be compared to the traditional approach of having five hot water bottles (https://en.wikipedia.org/wiki/Hot_water_bottle). From this point of view having 500 l of 80°C water sounds already quite generous.

[Juho]

Originally Posted by belizesailor

Ha, now just needs to be movable! Movable, heat sink/ballast. Make it a potable water tank too and now you have several uses!
[emoji6]

Maybe the potable water should indeed be in two tanks, one on the port side and one on starboard. That water would not be heated, but it could be pumped from one side to the other if the tanks are half full.

The idea of movable ballast made me wonder also if someone has used water filled fenders, tied with a long line somewhere in the middle of the boat. They could be quite easily thrown to the other side of the boat before (or after) each tack.

[Juho]

Originally Posted by Dockhead

I guess you could put a thermostat in THAT circuit, too, couldn't you. A couple of degrees less than the main thermostat.

I'm not an expert of car/boat cooling systems (i.e. if there are additional thermostats in the motors already today) but this sounds like the correct approach. Flushing heat to the sea should take place only when there is too much heat to be used by the other systems. And the motor should keep all its heat until it is above its minimum running temperature.

[a64pilot]

Originally Posted by Dockhead

I guess you could put a thermostat in THAT circuit, too, couldn't you. A couple of degrees less than the main thermostat.

I guess you could or what I was saying was that with a ball valve, you could be the thermostat. It’s probably unlikely that your heat exchanger in the water tank would be so efficient that it would overcool the engine though
But enough surface area and it could.
But this is all sort of just knocking things around too, what does a Diesel heater burn overnight? We could keep a GP medium tent warm with our stove with a 5 gl can of Diesel and that stove would get red hot, it’s hard to heat a tent .

[a64pilot]

Originally Posted by Juho

I'm not an expert of car/boat cooling systems (i.e. if there are additional thermostats in the motors already today) but this sounds like the correct approach. Flushing heat to the sea should take place only when there is too much heat to be used by the other systems. And the motor should keep all its heat until it is above its minimum running temperature.

Duramax Diesel has two thermostats, I believe it’s to ease the motor into warming up and not hit it with a slug of cold water and to allow it to stay warmer better under light loads where it spends most of its life.
Multiple thermostats are not uncommon.
https://www.agriculture.com/machiner...form=hootsuite

[Dockhead]

Originally Posted by a64pilot

. . . But this is all sort of just knocking things around too, what does a Diesel heater burn overnight? We could keep a GP medium tent warm with our stove with a 5 gl can of Diesel and that stove would get red hot, it’s hard to heat a tent .

0.2 l/h on low. 1.2 l/h on high. So I don't know -- 5 liters overnight, on average?

[a64pilot]

Just wondering if all that expense and complexity was worth the fuel savings. Especially when you figure out how many nights per year that you are burning 5L a night, then will the water carry you all night, and do you motor every day long enough to heat enough water to get you thorough the night?
Interesting thought exercise sort of along the line of having a massive lithium battery bank to replace a generator or at least to reduce generator run hours. Sure you can do it, and with an automatic generator start you can do so without having to babysit it, but it’s likely it would never pay for itself.
Doesn’t hurt to have something to talk about on a Sunday afternoon though.

[Dockhead]

Originally Posted by a64pilot

Just wondering if all that expense and complexity was worth the fuel savings. Especially when you figure out how many nights per year that you are burning 5L a night, then will the water carry you all night, and do you motor every day long enough to heat enough water to get you thorough the night?
Interesting thought exercise sort of along the line of having a massive lithium battery bank to replace a generator or at least to reduce generator run hours. Sure you can do it, and with an automatic generator start you can do so without having to babysit it, but it’s likely it would never pay for itself.
Doesn’t hurt to have something to talk about on a Sunday afternoon though.

I agree with you. And that's why I haven't done anything like this.


But if you are new building, it might look somewhat different.