This may be somewhat repetitive of a mixture of posts, but it works well for me, is inexpensive, low tech, and is an easy way to monitor boiler performance, while being adaptable to most systems.
My system: Termovar thermostatic mixing valve and plate hx to pressurized storage/system.
Monitoring sensors: probe type meat or food thermometers. The ones I like the best are the Espresso Milk Frothing Thermometer type, with a range of 40-220F and a 2 inch dial, easy to read. They run about $6 on e-bay.
Monitor points: 1) boiler input to hx and 2) hx return to boiler; 3) hx output to system and 4) system return to hx; 5) boiler return. Cable tie the probe to a section of pipe at each location, wrap with insulation.
Performance: At a glance you can determine all of the following. 1) boiler return water temp – let’s you know whether return is at about the desired 160; aids in adjusting the return protection mixing valve. 2) delta T on both the boiler and system sides of the hx. 3) boiler side of hx delta T – let’s you know actual temp boiler is delivering to the hx and the water temp the hx is returning to the boiler, how the temp rises and falls as boiler may cycle or wood load burns, and how much relative heat is being extracted to the system. 4) system side of hx delta T – let’s you know actual temp hx is delivering to the system and the water temp the system is returning to the hx, how the temp rises and falls as boiler may cycle or wood load burns, how much heat is being used by the system, and the relative hx efficiency at various temps.
Interesting btu calculation: if you know or assume a gal/min flow on the system side of the hx, you can easily determine btu’s being delivered to the system. Formula: gal/min x 60 x 8.35 lbs/gal x delta T system side of hx = btu/hr. Example: assume 5 gallons/minute and delta T of 40. 5 x 60 x 8.35 x 40 = 100,200 btu/hr. If the flow is 8 gal/min, then btus = 160,320. If delta T is 20 and flow is 8 gal/min, then btus = 80,160.
Observation: assume boiler at operating temp range (170-190F). As system input to hx rises, delta T on system side of hx closes. For my system, the maximum system side delta T will be just about 45. That occurs when boiler input to hx is close 190 and system input to hx is 110 (or below). Hx output to system will be 155 in this example. As system input to hx rises above 110, given same boiler input to hx, hx output to system will rise but the delta T will close.
Complication: with the Termovar or other mixing valve for return water protection, it gets complicated to calculate actual boiler btu output to the hx (or system if no hx), as part of the boiler water is being delivered to the system and part is being cycled back to the boiler. Without actually knowing the gal/min on the system side of the mixing valve and the delta T on output to system and system return to the mixing valve, I don’t know how to calculate btu’s being delivered to the system. Maybe someone else has an idea on this.
Hope this is useful.
My system: Termovar thermostatic mixing valve and plate hx to pressurized storage/system.
Monitoring sensors: probe type meat or food thermometers. The ones I like the best are the Espresso Milk Frothing Thermometer type, with a range of 40-220F and a 2 inch dial, easy to read. They run about $6 on e-bay.
Monitor points: 1) boiler input to hx and 2) hx return to boiler; 3) hx output to system and 4) system return to hx; 5) boiler return. Cable tie the probe to a section of pipe at each location, wrap with insulation.
Performance: At a glance you can determine all of the following. 1) boiler return water temp – let’s you know whether return is at about the desired 160; aids in adjusting the return protection mixing valve. 2) delta T on both the boiler and system sides of the hx. 3) boiler side of hx delta T – let’s you know actual temp boiler is delivering to the hx and the water temp the hx is returning to the boiler, how the temp rises and falls as boiler may cycle or wood load burns, and how much relative heat is being extracted to the system. 4) system side of hx delta T – let’s you know actual temp hx is delivering to the system and the water temp the system is returning to the hx, how the temp rises and falls as boiler may cycle or wood load burns, how much heat is being used by the system, and the relative hx efficiency at various temps.
Interesting btu calculation: if you know or assume a gal/min flow on the system side of the hx, you can easily determine btu’s being delivered to the system. Formula: gal/min x 60 x 8.35 lbs/gal x delta T system side of hx = btu/hr. Example: assume 5 gallons/minute and delta T of 40. 5 x 60 x 8.35 x 40 = 100,200 btu/hr. If the flow is 8 gal/min, then btus = 160,320. If delta T is 20 and flow is 8 gal/min, then btus = 80,160.
Observation: assume boiler at operating temp range (170-190F). As system input to hx rises, delta T on system side of hx closes. For my system, the maximum system side delta T will be just about 45. That occurs when boiler input to hx is close 190 and system input to hx is 110 (or below). Hx output to system will be 155 in this example. As system input to hx rises above 110, given same boiler input to hx, hx output to system will rise but the delta T will close.
Complication: with the Termovar or other mixing valve for return water protection, it gets complicated to calculate actual boiler btu output to the hx (or system if no hx), as part of the boiler water is being delivered to the system and part is being cycled back to the boiler. Without actually knowing the gal/min on the system side of the mixing valve and the delta T on output to system and system return to the mixing valve, I don’t know how to calculate btu’s being delivered to the system. Maybe someone else has an idea on this.
Hope this is useful.
