Pre Heater / Block heaters

if I am using Tee Pieces surely unless the circulation pump is running then the very fact that the pump isnt running will mean most of the coolant will run over the Tee ?

palace said:

if I am using Tee Pieces surely unless the circulation pump is running then the very fact that the pump isnt running will mean most of the coolant will run over the Tee ?

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the water will flow along the path of least resistance most but will flow to an extent in every direction and the same will happen with the block heater pump running so you will have no control of where the heat goes.

Sean said:

yes it will, the ''block heater'' will be out in the fresh air and will loose heat - thus reducing the available heat for the interior heater matrix

unless it's really well insulated

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The heat loss from the block heater will be very small compared to that of the heater matrix. Maybe 5% at most but there would be no harm in insulating it. I might do the maths and actually get a figure for it.

All our standby gen sets have a block water heater, it works by convection, with a cold water feed at the bottom and a hot outlet at the top, we get them in 110V or 220V, thay are mounted vertically next to the engine and are connected with half inch (internal ) standard rubber hoses, no special fitting, They are pretty much what you have described, basically an emersion heater in a steel enclosure with a fitted thermostat. I was trying to find a cost but so far no luck, but they are out there. pre-made no fancy build or connections to worry about.

IanFiTheDwarf said:

The heat loss from the block heater will be very small compared to that of the heater matrix. Maybe 5% at most but there would be no harm in insulating it. I might do the maths and actually get a figure for it.

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feel free to prove a few decades of practical experience wrong with your maths, I'll even let you borrow my slide rule

Using a simple heat loss calculation which is meant for horizontal pipes but will be close enough for our purposes since our block heater is really just a short piece of un-insulated horizontal pipe when it is switched off.

Heat loss Q = h A ∆T in BTU/hr

Where

h is the coefficient of heat transfer

A is the surface area in ft2

∆T is the difference between the air temperature and the surface temperature in deg F


I have stuck with 18 as the coefficient of heat transfer as this is what is used for horizontal pipes in free air but it could be lower as the under bonnet air is somewhat enclosed but will be higher if there is a flow of air due to the car moving. (The possible range is 2-25 btw)

I have worked out the surface area of my heater is 0.8 ft²

I will use 0°C (32°F) for the under bonnet air temperature and 80°C (167°F) for the water temperature leaving the heater matrix as these are what I would consider the extremes with an engine running and the heater fan on

Therefore

Q = 18 x 0.8 x 144
=2073.6 btu/hr

If you consider that the maximum heat output (fan on full and vents open) of an average heater matrix is about 60,000 btu/hr then the block heater would loose an additional 3.5% more heat than the heater matrix.

But if you look at it while the block heater is heating the engine or defrosting the windows then if you are still loosing 2073 btu/hr that is about 600 watts, 20% of the heat you are putting in so it would be a good idea to insulate the heater.

Slide rule not required!

60,000 btu/hr !!!!!!!!!!!!!!!!!!!!!!

I wish

i assume i would need to mount the heater and pump below the heater matrix as the pump will not be self priming ?

palace said:

i assume i would need to mount the heater and pump below the heater matrix as the pump will not be self priming ?

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As long as its below the minimum level mark in the expansion tank it will bleed threw.

Sean said:

60,000 btu/hr !!!!!!!!!!!!!!!!!!!!!!

I wish

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Maybe 60,000 btu is a bit optimistic, its just what kept coming up when I googled for car heater output.

Could be close for a discovery but maybe more like 6000 for your series 3!

IanFiTheDwarf said:

Using a simple heat loss calculation which is meant for horizontal pipes but will be close enough for our purposes since our block heater is really just a short piece of un-insulated horizontal pipe when it is switched off.

Heat loss Q = h A ∆T in BTU/hr

Where

h is the coefficient of heat transfer

A is the surface area in ft2

∆T is the difference between the air temperature and the surface temperature in deg F


I have stuck with 18 as the coefficient of heat transfer as this is what is used for horizontal pipes in free air but it could be lower as the under bonnet air is somewhat enclosed but will be higher if there is a flow of air due to the car moving. (The possible range is 2-25 btw)

I have worked out the surface area of my heater is 0.8 ft²

I will use 0°C (32°F) for the under bonnet air temperature and 80°C (167°F) for the water temperature leaving the heater matrix as these are what I would consider the extremes with an engine running and the heater fan on

Therefore

Q = 18 x 0.8 x 144
=2073.6 btu/hr

If you consider that the maximum heat output (fan on full and vents open) of an average heater matrix is about 60,000 btu/hr then the block heater would loose an additional 3.5% more heat than the heater matrix.

But if you look at it while the block heater is heating the engine or defrosting the windows then if you are still loosing 2073 btu/hr that is about 600 watts, 20% of the heat you are putting in so it would be a good idea to insulate the heater.

Slide rule not required!

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You left the wind chill factor out at 60 mph would be like 10F

i'm looking at building a preheater too, i have had the webasto type on a p38, excellent system but can be temperamental.

ive been toying with the idea of using a dishwasher flowthru heater with a thermostat (probably from maplins) all mounted in a sealable metal box.

obviously it would be 240v but the heater can be obtained very cheap, couple with a 12v auxiliary pump (if i cant find a 240v one suitable) i reckon it can be done for under 50 quid!!

heres the heater WATER HEATER ELEMENT UNIT - WHIRLPOOL DISHWASHER | eBay

That's defiantly doable but I think they are only about 2kw so would need a longer preheat but it would reduce your power requirements. I am having trouble finding waterproof connectors which can take the full 3kw which aren't absolutely huge.

I have seen some nice small 10A connectors designed for garden lighting.

IanFiTheDwarf said:

Maybe 60,000 btu is a bit optimistic, its just what kept coming up when I googled for car heater output.

Could be close for a discovery but maybe more like 6000 for your series 3!

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i suspect you are talking out of your arse, go look at the heat output of some domestic rads, compare them against the surface area of a standard landy exchanger and come back with another guess regarding the BTU component of your equation

you could heat a house with 60,000 BTUs

Sean said:

i suspect you are talking out of your arse, go look at the heat output of some domestic rads, compare them against the surface area of a standard landy exchanger and come back with another guess regarding the BTU component of your equation

you could heat a house with 60,000 BTUs

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And you don't know your arse from your elbow! A house radiator is not the same as a heater matrix or a car radiator. A heater matrix probably has close to 2 square meters of surface area including all the aluminium fins between the plates, has water taken from the hottest part of the engine running threw it and most importantly has forced airflow over its surface. A house radiator is rated for water at something like 60 deg C and has only convection to to move air over its surface. You could compare a car heater to a small house radiator if you don't switch the fan on but but you won't defrosted your Windows very fast that way.

go find the output in BTUs of a 2 meter x 800mm house rad - just for fun eh

then come back and have another guess at the output of a landy exchanger

As I said its not the same thing. Forced air makes all the difference

IanFiTheDwarf said:

As I said its not the same thing. Forced air makes all the difference

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I KNOW !

more custard rendering

dont know if this info help you chaps but you can get 24v or other voltage Imersion heater elements of a guy on ebay


wiht a few cheap plumbing fixtures and some copper pipe should be easy to make up a heater

I dont have any connection to this guy but Ive have been thinking along the same lines.

But my idea was to use a windturbine to generate most of the power ie overnight and mains to 24volt power supply when no wind or on timer b4 i go out to work

here are my basic outlines

windturbine made from a wheel hub and some bits from these guys
http://www.forcefieldmagnets.com( well worth reading)

a small battery bank in garage to take the charge when car not hooked up.
i power supply to give me 24 volts when little wind or for a boost

heater element of about 500watts req about 20amps 24volts

put the bits together and you have a block heater